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# 11. API Reference

## 11.1. `distutils.core` — Core Distutils functionality

The `distutils.core` module is the only module that needs to be installed to use the Distutils. It provides the `setup()` (which is called from the setup script). Indirectly provides the `distutils.dist.Distribution` and `distutils.cmd.Command` class.

`distutils.core.``setup`(arguments)

  The basic do-everything function that does most everything you could ever ask for from a Distutils method. See XXXXX

  The setup function takes a large number of arguments. These are laid out in the following table.

  argument name | value | type
  --- | --- | ---
  name | The name of the package | a string
  version | The version number of the package | See `distutils.version`
  description | A single line describing the package | a string
  long_description | Longer description of the package | a string
  author | The name of the package author | a string
  author_email | The email address of the package author | a string
  maintainer | The name of the current maintainer, if different from the author | a string
  maintainer_email | The email address of the current maintainer, if different from the author |
  url | A URL for the package (homepage) | a URL
  download_url | A URL to download the package | a URL
  packages | A list of Python packages that distutils will manipulate | a list of strings
  py_modules | A list of Python modules that distutils will manipulate | a list of strings
  scripts | A list of standalone script files to be built and installed | a list of strings
  ext_modules | A list of Python extensions to be built | A list of instances of `distutils.core.Extension`
  classifiers | A list of categories for the package | The list of available categorizations is at http://pypi.python.org/pypi?:action=list_classifiers.
  distclass | the `Distribution` class to use | A subclass of `distutils.core.Distribution`
  script_name | The name of the setup.py script - defaults to `sys.argv[0]` | a string
  script_args | Arguments to supply to the setup script | a list of strings
  options | default options for the setup script | a string
  license | The license for the package | a string
  keywords | Descriptive meta-data, see PEP 314 |
  platforms |  |
  cmdclass | A mapping of command names to `Command` subclasses | a dictionary
  data_files | A list of data files to install | a list
  package_dir | A mapping of package to directory names | a dictionary

`distutils.core.``run_setup`(script_name[, script_args=None, stop_after='run'])

  Run a setup script in a somewhat controlled environment, and return the `distutils.dist.Distribution` instance that drives things. This is useful if you need to find out the distribution meta-data (passed as keyword args from script to `setup()`), or the contents of the config files or command-line.

  script_name is a file that will be run with `execfile()` `sys.argv[0]` will be replaced with script for the duration of the call. script_args is a list of strings; if supplied, `sys.argv[1:]` will be replaced by script_args for the duration of the call.

  stop_after tells `setup()` when to stop processing; possible values:

  value | description
  --- | ---
  init | Stop after the `Distribution` instance has been created and populated with the keyword arguments to `setup()`
  config | Stop after config files have been parsed (and their data stored in the `Distribution` instance)
  commandline | Stop after the command-line (`sys.argv[1:]` or script_args) have been parsed (and the data stored in the `Distribution` instance.)
  run | Stop after all commands have been run (the same as if `setup()` had been called in the usual way). This is the default value.

In addition, the `distutils.core` module exposed a number of classes that live elsewhere.

- `Extension` from `distutils.extension`
- `Command` from `distutils.cmd`
- `Distribution` from `distutils.dist`

A short description of each of these follows, but see the relevant module for the full reference.

class `distutils.core.``Extension`

  The Extension class describes a single C or C++extension module in a setup script. It accepts the following keyword arguments in its constructor

  argument name | value | type
  --- | --- | ---
  name | the full name of the extension, including any packages — ie. not a filename or pathname, but Python dotted name | string
  sources | list of source filenames, relative to the distribution root (where the setup script lives), in Unix form (slash- separated) for portability. Source files may be C, C++, SWIG (.i), platform-specific resource files, or whatever else is recognized by the build_ext command as source for a Python extension. | string
  include_dirs | list of directories to search for C/C++ header files (in Unix form for portability) | string
  define_macros | list of macros to define; each macro is defined using a 2-tuple `(name, value)`, where value is either the string to define it to or `None` to define it without a particular value (equivalent of `#define FOO` in source or -DFOO on Unix C compiler command line) | (string, string) tuple or (name, `None`)
  undef_macros | list of macros to undefine explicitly | string
  library_dirs | list of directories to search for C/C++ libraries at link time | string
  libraries | list of library names (not filenames or paths) to link against | string
  runtime_library_dirs | list of directories to search for C/C++ libraries at run time (for shared extensions, this is when the extension is loaded) | string
  extra_objects | list of extra files to link with (eg. object files not implied by ‘sources’, static library that must be explicitly specified, binary resource files, etc.) | string
  extra_compile_args | any extra platform- and compiler-specific information to use when compiling the source files in ‘sources’. For platforms and compilers where a command line makes sense, this is typically a list of command-line arguments, but for other platforms it could be anything. | string
  extra_link_args | any extra platform- and compiler-specific information to use when linking object files together to create the extension (or to create a new static Python interpreter). Similar interpretation as for ‘extra_compile_args’. | string
  export_symbols | list of symbols to be exported from a shared extension. Not used on all platforms, and not generally necessary for Python extensions, which typically export exactly one symbol: `init` + extension_name. | string
  depends | list of files that the extension depends on | string
  language | extension language (i.e. `'c'`, `'c++'`, `'objc'`). Will be detected from the source extensions if not provided. | string

class `distutils.core.``Distribution`

  A `Distribution` describes how to build, install and package up a Python software package.

  See the `setup()` function for a list of keyword arguments accepted by the Distribution constructor. `setup()` creates a Distribution instance.

class `distutils.core.``Command`
  A `Command` class (or rather, an instance of one of its subclasses) implement a single distutils command.

## 11.2. `distutils.ccompiler` — CCompiler base class

This module provides the abstract base class for the `CCompiler` classes. A `CCompiler` instance can be used for all the compile and link steps needed to build a single project. Methods are provided to set options for the compiler — macro definitions, include directories, link path, libraries and the like.

This module provides the following functions.

`distutils.ccompiler.``gen_lib_options`(compiler, library_dirs, runtime_library_dirs, libraries)
  Generate linker options for searching library directories and linking with specific libraries. libraries and library_dirs are, respectively, lists of library names (not filenames!) and search directories. Returns a list of command-line options suitable for use with some compiler (depending on the two format strings passed in).

`distutils.ccompiler.``gen_preprocess_options`(macros, include_dirs)
  Generate C pre-processor options (-D, -U, -I) as used by at least two types of compilers: the typical Unix compiler and Visual C++. macros is the usual thing, a list of 1- or 2-tuples, where `(name,)` means undefine (-U) macro name, and `(name, value)` means define (-D) macro name to value. include_dirs is just a list of directory names to be added to the header file search path (-I). Returns a list of command-line options suitable for either Unix compilers or Visual C++.

`distutils.ccompiler.``get_default_compiler`(osname, platform)

  Determine the default compiler to use for the given platform.

  osname should be one of the standard Python OS names (i.e. the ones returned by `os.name`) and platform the common value returned by `sys.platform` for the platform in question.

  The default values are `os.name` and `sys.platform` in case the parameters are not given.

`distutils.ccompiler.``new_compiler`(plat=None, compiler=None, verbose=0, dry_run=0, force=0)
  Factory function to generate an instance of some CCompiler subclass for the supplied platform/compiler combination. plat defaults to `os.name` (eg. `'posix'`, `'nt'`), and compiler defaults to the default compiler for that platform. Currently only `'posix'` and `'nt'` are supported, and the default compilers are “traditional Unix interface” (`UnixCCompiler` class) and Visual C++ (`MSVCCompiler` class). Note that it’s perfectly possible to ask for a Unix compiler object under Windows, and a Microsoft compiler object under Unix—if you supply a value for compiler, plat is ignored.

`distutils.ccompiler.``show_compilers`()
  Print list of available compilers (used by the --help-compiler options to build, build_ext, build_clib).

class `distutils.ccompiler.``CCompiler`([verbose=0, dry_run=0, force=0])

  The abstract base class `CCompiler` defines the interface that must be implemented by real compiler classes. The class also has some utility methods used by several compiler classes.

  The basic idea behind a compiler abstraction class is that each instance can be used for all the compile/link steps in building a single project. Thus, attributes common to all of those compile and link steps — include directories, macros to define, libraries to link against, etc. — are attributes of the compiler instance. To allow for variability in how individual files are treated, most of those attributes may be varied on a per-compilation or per-link basis.

  The constructor for each subclass creates an instance of the Compiler object. Flags are verbose (show verbose output), dry_run (don’t actually execute the steps) and force (rebuild everything, regardless of dependencies). All of these flags default to `0` (off). Note that you probably don’t want to instantiate `CCompiler` or one of its subclasses directly - use the `distutils.CCompiler.new_compiler()` factory function instead.

  The following methods allow you to manually alter compiler options for the instance of the Compiler class.

  `add_include_dir`(dir)
    Add dir to the list of directories that will be searched for header files. The compiler is instructed to search directories in the order in which they are supplied by successive calls to `add_include_dir()`.
  `set_include_dirs`(dirs)
    Set the list of directories that will be searched to dirs (a list of strings). Overrides any preceding calls to `add_include_dir()`; subsequent calls to `add_include_dir()` add to the list passed to `set_include_dirs()`. This does not affect any list of standard include directories that the compiler may search by default.
  `add_library`(libname)

    Add libname to the list of libraries that will be included in all links driven by this compiler object. Note that libname should *not* be the name of a file containing a library, but the name of the library itself: the actual filename will be inferred by the linker, the compiler, or the compiler class (depending on the platform).

    The linker will be instructed to link against libraries in the order they were supplied to `add_library()` and/or `set_libraries()`. It is perfectly valid to duplicate library names; the linker will be instructed to link against libraries as many times as they are mentioned.

  `set_libraries`(libnames)
    Set the list of libraries to be included in all links driven by this compiler object to libnames (a list of strings). This does not affect any standard system libraries that the linker may include by default.
  `add_library_dir`(dir)
    Add dir to the list of directories that will be searched for libraries specified to `add_library()` and `set_libraries()`. The linker will be instructed to search for libraries in the order they are supplied to `add_library_dir()` and/or `set_library_dirs()`.
  `set_library_dirs`(dirs)
    Set the list of library search directories to dirs (a list of strings). This does not affect any standard library search path that the linker may search by default.
  `add_runtime_library_dir`(dir)
    Add dir to the list of directories that will be searched for shared libraries at runtime.
  `set_runtime_library_dirs`(dirs)
    Set the list of directories to search for shared libraries at runtime to dirs (a list of strings). This does not affect any standard search path that the runtime linker may search by default.
  `define_macro`(name[, value=None])
    Define a preprocessor macro for all compilations driven by this compiler object. The optional parameter value should be a string; if it is not supplied, then the macro will be defined without an explicit value and the exact outcome depends on the compiler used (XXX true? does ANSI say anything about this?)
  `undefine_macro`(name)
    Undefine a preprocessor macro for all compilations driven by this compiler object. If the same macro is defined by `define_macro()` and undefined by `undefine_macro()` the last call takes precedence (including multiple redefinitions or undefinitions). If the macro is redefined/undefined on a per-compilation basis (ie. in the call to `compile()`), then that takes precedence.
  `add_link_object`(object)
    Add object to the list of object files (or analogues, such as explicitly named library files or the output of “resource compilers”) to be included in every link driven by this compiler object.
  `set_link_objects`(objects)
    Set the list of object files (or analogues) to be included in every link to objects. This does not affect any standard object files that the linker may include by default (such as system libraries).

  The following methods implement methods for autodetection of compiler options, providing some functionality similar to GNU autoconf.

  `detect_language`(sources)
    Detect the language of a given file, or list of files. Uses the instance attributes `language_map` (a dictionary), and `language_order` (a list) to do the job.
  `find_library_file`(dirs, lib[, debug=0])
    Search the specified list of directories for a static or shared library file lib and return the full path to that file. If debug is true, look for a debugging version (if that makes sense on the current platform). Return `None` if lib wasn’t found in any of the specified directories.
  `has_function`(funcname[, includes=None, include_dirs=None, libraries=None, library_dirs=None])
    Return a boolean indicating whether funcname is supported on the current platform. The optional arguments can be used to augment the compilation environment by providing additional include files and paths and libraries and paths.
  `library_dir_option`(dir)
    Return the compiler option to add dir to the list of directories searched for libraries.
  `library_option`(lib)
    Return the compiler option to add dir to the list of libraries linked into the shared library or executable.
  `runtime_library_dir_option`(dir)
    Return the compiler option to add dir to the list of directories searched for runtime libraries.
  `set_executables`(**args)

    Define the executables (and options for them) that will be run to perform the various stages of compilation. The exact set of executables that may be specified here depends on the compiler class (via the ‘executables’ class attribute), but most will have:

    attribute | description
    --- | ---
    compiler | the C/C++ compiler
    linker_so | linker used to create shared objects and libraries
    linker_exe | linker used to create binary executables
    archiver | static library creator

    On platforms with a command-line (Unix, DOS/Windows), each of these is a string that will be split into executable name and (optional) list of arguments. (Splitting the string is done similarly to how Unix shells operate: words are delimited by spaces, but quotes and backslashes can override this. See `distutils.util.split_quoted()`.)

  The following methods invoke stages in the build process.

  `compile`(sources[, output_dir=None, macros=None, include_dirs=None, debug=0, extra_preargs=None, extra_postargs=None, depends=None])

    Compile one or more source files. Generates object files (e.g. transforms a `.c` file to a `.o` file.)

    sources must be a list of filenames, most likely C/C++ files, but in reality anything that can be handled by a particular compiler and compiler class (eg. `MSVCCompiler` can handle resource files in sources). Return a list of object filenames, one per source filename in sources. Depending on the implementation, not all source files will necessarily be compiled, but all corresponding object filenames will be returned.

    If output_dir is given, object files will be put under it, while retaining their original path component. That is, `foo/bar.c` normally compiles to `foo/bar.o` (for a Unix implementation); if output_dir is build, then it would compile to `build/foo/bar.o`.

    macros, if given, must be a list of macro definitions. A macro definition is either a `(name, value)` 2-tuple or a `(name,)` 1-tuple. The former defines a macro; if the value is `None`, the macro is defined without an explicit value. The 1-tuple case undefines a macro. Later definitions/redefinitions/undefinitions take precedence.

    include_dirs, if given, must be a list of strings, the directories to add to the default include file search path for this compilation only.

    debug is a boolean; if true, the compiler will be instructed to output debug symbols in (or alongside) the object file(s).

    extra_preargs and extra_postargs are implementation-dependent. On platforms that have the notion of a command-line (e.g. Unix, DOS/Windows), they are most likely lists of strings: extra command-line arguments to prepend/append to the compiler command line. On other platforms, consult the implementation class documentation. In any event, they are intended as an escape hatch for those occasions when the abstract compiler framework doesn’t cut the mustard.

    depends, if given, is a list of filenames that all targets depend on. If a source file is older than any file in depends, then the source file will be recompiled. This supports dependency tracking, but only at a coarse granularity.

    Raises `CompileError` on failure.

  `create_static_lib`(objects, output_libname[, output_dir=None, debug=0, target_lang=None])

    Link a bunch of stuff together to create a static library file. The “bunch of stuff” consists of the list of object files supplied as objects, the extra object files supplied to `add_link_object()` and/or `set_link_objects()`, the libraries supplied to `add_library()` and/or `set_libraries()`, and the libraries supplied as libraries (if any).

    output_libname should be a library name, not a filename; the filename will be inferred from the library name. output_dir is the directory where the library file will be put. XXX defaults to what?

    debug is a boolean; if true, debugging information will be included in the library (note that on most platforms, it is the compile step where this matters: the debug flag is included here just for consistency).

    target_lang is the target language for which the given objects are being compiled. This allows specific linkage time treatment of certain languages.

    Raises `LibError` on failure.

  `link`(target_desc, objects, output_filename[, output_dir=None, libraries=None, library_dirs=None, runtime_library_dirs=None, export_symbols=None, debug=0, extra_preargs=None, extra_postargs=None, build_temp=None, target_lang=None])

    Link a bunch of stuff together to create an executable or shared library file.

    The “bunch of stuff” consists of the list of object files supplied as objects. output_filename should be a filename. If output_dir is supplied, output_filename is relative to it (i.e. output_filename can provide directory components if needed).

    libraries is a list of libraries to link against. These are library names, not filenames, since they’re translated into filenames in a platform-specific way (eg. foo becomes `libfoo.a` on Unix and `foo.lib` on DOS/Windows). However, they can include a directory component, which means the linker will look in that specific directory rather than searching all the normal locations.

    library_dirs, if supplied, should be a list of directories to search for libraries that were specified as bare library names (ie. no directory component). These are on top of the system default and those supplied to `add_library_dir()` and/or `set_library_dirs()`. runtime_library_dirs is a list of directories that will be embedded into the shared library and used to search for other shared libraries that *it* depends on at run-time. (This may only be relevant on Unix.)

    export_symbols is a list of symbols that the shared library will export. (This appears to be relevant only on Windows.)

    debug is as for `compile()` and `create_static_lib()`, with the slight distinction that it actually matters on most platforms (as opposed to `create_static_lib()`, which includes a debug flag mostly for form’s sake).

    extra_preargs and extra_postargs are as for `compile()` (except of course that they supply command-line arguments for the particular linker being used).

    target_lang is the target language for which the given objects are being compiled. This allows specific linkage time treatment of certain languages.

    Raises `LinkError` on failure.

  `link_executable`(objects, output_progname[, output_dir=None, libraries=None, library_dirs=None, runtime_library_dirs=None, debug=0, extra_preargs=None, extra_postargs=None, target_lang=None])
    Link an executable. output_progname is the name of the file executable, while objects are a list of object filenames to link in. Other arguments are as for the `link()` method.
  `link_shared_lib`(objects, output_libname[, output_dir=None, libraries=None, library_dirs=None, runtime_library_dirs=None, export_symbols=None, debug=0, extra_preargs=None, extra_postargs=None, build_temp=None, target_lang=None])
    Link a shared library. output_libname is the name of the output library, while objects is a list of object filenames to link in. Other arguments are as for the `link()` method.
  `link_shared_object`(objects, output_filename[, output_dir=None, libraries=None, library_dirs=None, runtime_library_dirs=None, export_symbols=None, debug=0, extra_preargs=None, extra_postargs=None, build_temp=None, target_lang=None])
    Link a shared object. output_filename is the name of the shared object that will be created, while objects is a list of object filenames to link in. Other arguments are as for the `link()` method.
  `preprocess`(source[, output_file=None, macros=None, include_dirs=None, extra_preargs=None, extra_postargs=None])

    Preprocess a single C/C++ source file, named in source. Output will be written to file named output_file, or stdout if output_file not supplied. macros is a list of macro definitions as for `compile()`, which will augment the macros set with `define_macro()` and `undefine_macro()`. include_dirs is a list of directory names that will be added to the default list, in the same way as `add_include_dir()`.

    Raises `PreprocessError` on failure.

  The following utility methods are defined by the `CCompiler` class, for use by the various concrete subclasses.

  `executable_filename`(basename[, strip_dir=0, output_dir=''])
    Returns the filename of the executable for the given basename. Typically for non-Windows platforms this is the same as the basename, while Windows will get a `.exe` added.
  `library_filename`(libname[, lib_type='static', strip_dir=0, output_dir=''])
    Returns the filename for the given library name on the current platform. On Unix a library with lib_type of `'static'` will typically be of the form `liblibname.a`, while a lib_type of `'dynamic'` will be of the form `liblibname.so`.
  `object_filenames`(source_filenames[, strip_dir=0, output_dir=''])
    Returns the name of the object files for the given source files. source_filenames should be a list of filenames.
  `shared_object_filename`(basename[, strip_dir=0, output_dir=''])
    Returns the name of a shared object file for the given file name basename.
  `execute`(func, args[, msg=None, level=1])
    Invokes `distutils.util.execute()` This method invokes a Python function func with the given arguments args, after logging and taking into account the dry_run flag. XXX see also.
  `spawn`(cmd)
    Invokes `distutils.util.spawn()`. This invokes an external process to run the given command. XXX see also.
  `mkpath`(name[, mode=511])
    Invokes `distutils.dir_util.mkpath()`. This creates a directory and any missing ancestor directories. XXX see also.
  `move_file`(src, dst)
    Invokes `distutils.file_util.move_file()`. Renames src to dst. XXX see also.
  `announce`(msg[, level=1])
    Write a message using `distutils.log.debug()`. XXX see also.
  `warn`(msg)
    Write a warning message msg to standard error.
  `debug_print`(msg)
    If the debug flag is set on this `CCompiler` instance, print msg to standard output, otherwise do nothing.

## 11.3. `distutils.unixccompiler` — Unix C Compiler

This module provides the `UnixCCompiler` class, a subclass of `CCompiler` that handles the typical Unix-style command-line C compiler:

- macros defined with -Dname[=value]
- macros undefined with -Uname
- include search directories specified with -Idir
- libraries specified with -llib
- library search directories specified with -Ldir
- compile handled by cc (or similar) executable with -c option: compiles `.c` to `.o`
- link static library handled by ar command (possibly with ranlib)
- link shared library handled by cc -shared

## 11.4. `distutils.msvccompiler` — Microsoft Compiler

This module provides `MSVCCompiler`, an implementation of the abstract `CCompiler` class for Microsoft Visual Studio. Typically, extension modules need to be compiled with the same compiler that was used to compile Python. For Python 2.3 and earlier, the compiler was Visual Studio 6. For Python 2.4 and 2.5, the compiler is Visual Studio .NET 2003. The AMD64 and Itanium binaries are created using the Platform SDK.

`MSVCCompiler` will normally choose the right compiler, linker etc. on its own. To override this choice, the environment variables DISTUTILS_USE_SDK and MSSdk must be both set. MSSdk indicates that the current environment has been setup by the SDK’s `SetEnv.Cmd` script, or that the environment variables had been registered when the SDK was installed; DISTUTILS_USE_SDK indicates that the distutils user has made an explicit choice to override the compiler selection by `MSVCCompiler`.

## 11.5. `distutils.bcppcompiler` — Borland Compiler

This module provides `BorlandCCompiler`, an subclass of the abstract `CCompiler` class for the Borland C++ compiler.

## 11.6. `distutils.cygwincompiler` — Cygwin Compiler

This module provides the `CygwinCCompiler` class, a subclass of `UnixCCompiler` that handles the Cygwin port of the GNU C compiler to Windows. It also contains the Mingw32CCompiler class which handles the mingw32 port of GCC (same as cygwin in no-cygwin mode).

## 11.7. `distutils.emxccompiler` — OS/2 EMX Compiler

This module provides the EMXCCompiler class, a subclass of `UnixCCompiler` that handles the EMX port of the GNU C compiler to OS/2.

## 11.8. `distutils.mwerkscompiler` — Metrowerks CodeWarrior support

Contains `MWerksCompiler`, an implementation of the abstract `CCompiler` class for MetroWerks CodeWarrior on the pre-Mac OS X Macintosh. Needs work to support CW on Windows or Mac OS X.

## 11.9. `distutils.archive_util` — Archiving utilities

This module provides a few functions for creating archive files, such as tarballs or zipfiles.

`distutils.archive_util.``make_archive`(base_name, format[, root_dir=None, base_dir=None, verbose=0, dry_run=0])
  Create an archive file (eg. `zip` or `tar`). base_name is the name of the file to create, minus any format-specific extension; format is the archive format: one of `zip`, `tar`, `ztar`, or `gztar`. root_dir is a directory that will be the root directory of the archive; ie. we typically `chdir` into root_dir before creating the archive. base_dir is the directory where we start archiving from; ie. base_dir will be the common prefix of all files and directories in the archive. root_dir and base_dir both default to the current directory. Returns the name of the archive file.

`distutils.archive_util.``make_tarball`(base_name, base_dir[, compress='gzip', verbose=0, dry_run=0])
  ‘Create an (optional compressed) archive as a tar file from all files in and under base_dir. compress must be `'gzip'` (the default), `'compress'`, `'bzip2'`, or `None`. Both tar and the compression utility named by compress must be on the default program search path, so this is probably Unix-specific. The output tar file will be named `base_dir.tar`, possibly plus the appropriate compression extension (`.gz`, `.bz2` or `.Z`). Return the output filename.

`distutils.archive_util.``make_zipfile`(base_name, base_dir[, verbose=0, dry_run=0])
  Create a zip file from all files in and under base_dir. The output zip file will be named base_dir + `.zip`. Uses either the `zipfile` Python module (if available) or the InfoZIP `zip` utility (if installed and found on the default search path). If neither tool is available, raises `DistutilsExecError`. Returns the name of the output zip file.

## 11.10. `distutils.dep_util` — Dependency checking

This module provides functions for performing simple, timestamp-based dependency of files and groups of files; also, functions based entirely on such timestamp dependency analysis.

`distutils.dep_util.``newer`(source, target)
  Return true if source exists and is more recently modified than target, or if source exists and target doesn’t. Return false if both exist and target is the same age or newer than source. Raise `DistutilsFileError` if source does not exist.

`distutils.dep_util.``newer_pairwise`(sources, targets)
  Walk two filename lists in parallel, testing if each source is newer than its corresponding target. Return a pair of lists (sources, targets) where source is newer than target, according to the semantics of `newer()`

`distutils.dep_util.``newer_group`(sources, target[, missing='error'])
  Return true if target is out-of-date with respect to any file listed in sources In other words, if target exists and is newer than every file in sources, return false; otherwise return true. missing controls what we do when a source file is missing; the default (`'error'`) is to blow up with an `OSError` from inside `os.stat()`; if it is `'ignore'`, we silently drop any missing source files; if it is `'newer'`, any missing source files make us assume that target is out-of-date (this is handy in “dry-run” mode: it’ll make you pretend to carry out commands that wouldn’t work because inputs are missing, but that doesn’t matter because you’re not actually going to run the commands).

## 11.11. `distutils.dir_util` — Directory tree operations

This module provides functions for operating on directories and trees of directories.

`distutils.dir_util.``mkpath`(name[, mode=0777, verbose=0, dry_run=0])
  Create a directory and any missing ancestor directories. If the directory already exists (or if name is the empty string, which means the current directory, which of course exists), then do nothing. Raise `DistutilsFileError` if unable to create some directory along the way (eg. some sub-path exists, but is a file rather than a directory). If verbose is true, print a one-line summary of each mkdir to stdout. Return the list of directories actually created.

`distutils.dir_util.``create_tree`(base_dir, files[, mode=0777, verbose=0, dry_run=0])
  Create all the empty directories under base_dir needed to put files there. base_dir is just the a name of a directory which doesn’t necessarily exist yet; files is a list of filenames to be interpreted relative to base_dir. base_dir + the directory portion of every file in files will be created if it doesn’t already exist. mode, verbose and dry_run flags are as for `mkpath()`.

`distutils.dir_util.``copy_tree`(src, dst[, preserve_mode=1, preserve_times=1, preserve_symlinks=0, update=0, verbose=0, dry_run=0])

  Copy an entire directory tree src to a new location dst. Both src and dst must be directory names. If src is not a directory, raise `DistutilsFileError`. If dst does not exist, it is created with `mkpath()`. The end result of the copy is that every file in src is copied to dst, and directories under src are recursively copied to dst. Return the list of files that were copied or might have been copied, using their output name. The return value is unaffected by update or dry_run: it is simply the list of all files under src, with the names changed to be under dst.

  preserve_mode and preserve_times are the same as for `copy_file()` in `distutils.file_util`; note that they only apply to regular files, not to directories. If preserve_symlinks is true, symlinks will be copied as symlinks (on platforms that support them!); otherwise (the default), the destination of the symlink will be copied. update and verbose are the same as for `copy_file()`.

`distutils.dir_util.``remove_tree`(directory[, verbose=0, dry_run=0])
  Recursively remove directory and all files and directories underneath it. Any errors are ignored (apart from being reported to `sys.stdout` if verbose is true).

** Some of this could be replaced with the shutil module? **

## 11.12. `distutils.file_util` — Single file operations

This module contains some utility functions for operating on individual files.

`distutils.file_util.``copy_file`(src, dst[, preserve_mode=1, preserve_times=1, update=0, link=None, verbose=0, dry_run=0])

  Copy file src to dst. If dst is a directory, then src is copied there with the same name; otherwise, it must be a filename. (If the file exists, it will be ruthlessly clobbered.) If preserve_mode is true (the default), the file’s mode (type and permission bits, or whatever is analogous on the current platform) is copied. If preserve_times is true (the default), the last-modified and last-access times are copied as well. If update is true, src will only be copied if dst does not exist, or if dst does exist but is older than src.

  link allows you to make hard links (using `os.link()`) or symbolic links (using `os.symlink()`) instead of copying: set it to `'hard'` or `'sym'`; if it is `None` (the default), files are copied. Don’t set link on systems that don’t support it: `copy_file()` doesn’t check if hard or symbolic linking is available. It uses `_copy_file_contents()` to copy file contents.

  Return a tuple `(dest_name, copied)`: dest_name is the actual name of the output file, and copied is true if the file was copied (or would have been copied, if dry_run true).

`distutils.file_util.``move_file`(src, dst[, verbose, dry_run])

  Move file src to dst. If dst is a directory, the file will be moved into it with the same name; otherwise, src is just renamed to dst. Returns the new full name of the file.

  Warning

  Handles cross-device moves on Unix using `copy_file()`. What about other systems?

`distutils.file_util.``write_file`(filename, contents)
  Create a file called filename and write contents (a sequence of strings without line terminators) to it.

## 11.13. `distutils.util` — Miscellaneous other utility functions

This module contains other assorted bits and pieces that don’t fit into any other utility module.

`distutils.util.``get_platform`()

  Return a string that identifies the current platform. This is used mainly to distinguish platform-specific build directories and platform-specific built distributions. Typically includes the OS name and version and the architecture (as supplied by ‘os.uname()’), although the exact information included depends on the OS; eg. for IRIX the architecture isn’t particularly important (IRIX only runs on SGI hardware), but for Linux the kernel version isn’t particularly important.

  Examples of returned values:

  - `linux-i586`
  - `linux-alpha`
  - `solaris-2.6-sun4u`
  - `irix-5.3`
  - `irix64-6.2`

  For non-POSIX platforms, currently just returns `sys.platform`.

  For Mac OS X systems the OS version reflects the minimal version on which binaries will run (that is, the value of `MACOSX_DEPLOYMENT_TARGET` during the build of Python), not the OS version of the current system.

  For universal binary builds on Mac OS X the architecture value reflects the univeral binary status instead of the architecture of the current processor. For 32-bit universal binaries the architecture is `fat`, for 64-bit universal binaries the architecture is `fat64`, and for 4-way universal binaries the architecture is `universal`. Starting from Python 2.7 and Python 3.2 the architecture `fat3` is used for a 3-way universal build (ppc, i386, x86_64) and `intel` is used for a univeral build with the i386 and x86_64 architectures

  Examples of returned values on Mac OS X:

  - `macosx-10.3-ppc`
  - `macosx-10.3-fat`
  - `macosx-10.5-universal`
  - `macosx-10.6-intel`

`distutils.util.``convert_path`(pathname)
  Return ‘pathname’ as a name that will work on the native filesystem, i.e. split it on ‘/’ and put it back together again using the current directory separator. Needed because filenames in the setup script are always supplied in Unix style, and have to be converted to the local convention before we can actually use them in the filesystem. Raises `ValueError` on non-Unix-ish systems if pathname either starts or ends with a slash.

`distutils.util.``change_root`(new_root, pathname)
  Return pathname with new_root prepended. If pathname is relative, this is equivalent to `os.path.join(new_root,pathname)` Otherwise, it requires making pathname relative and then joining the two, which is tricky on DOS/Windows.

`distutils.util.``check_environ`()

  Ensure that ‘os.environ’ has all the environment variables we guarantee that users can use in config files, command-line options, etc. Currently this includes:

  - HOME - user’s home directory (Unix only)
  - PLAT - description of the current platform, including hardware and OS (see `get_platform()`)

`distutils.util.``subst_vars`(s, local_vars)

  Perform shell/Perl-style variable substitution on s. Every occurrence of `$` followed by a name is considered a variable, and variable is substituted by the value found in the local_vars dictionary, or in `os.environ` if it’s not in local_vars. os.environ is first checked/augmented to guarantee that it contains certain values: see `check_environ()`. Raise `ValueError` for any variables not found in either local_vars or `os.environ`.

  Note that this is not a fully-fledged string interpolation function. A valid `$variable` can consist only of upper and lower case letters, numbers and an underscore. No { } or ( ) style quoting is available.

`distutils.util.``grok_environment_error`(exc[, prefix='error: '])
  Generate a useful error message from an `EnvironmentError` (`IOError` or `OSError`) exception object. Handles Python 1.5.1 and later styles, and does what it can to deal with exception objects that don’t have a filename (which happens when the error is due to a two-file operation, such as `rename()` or `link()`). Returns the error message as a string prefixed with prefix.

`distutils.util.``split_quoted`(s)
  Split a string up according to Unix shell-like rules for quotes and backslashes. In short: words are delimited by spaces, as long as those spaces are not escaped by a backslash, or inside a quoted string. Single and double quotes are equivalent, and the quote characters can be backslash-escaped. The backslash is stripped from any two-character escape sequence, leaving only the escaped character. The quote characters are stripped from any quoted string. Returns a list of words.

`distutils.util.``execute`(func, args[, msg=None, verbose=0, dry_run=0])
  Perform some action that affects the outside world (for instance, writing to the filesystem). Such actions are special because they are disabled by the dry_run flag. This method takes care of all that bureaucracy for you; all you have to do is supply the function to call and an argument tuple for it (to embody the “external action” being performed), and an optional message to print.

`distutils.util.``strtobool`(val)

  Convert a string representation of truth to true (1) or false (0).

  True values are `y`, `yes`, `t`, `true`, `on` and `1`; false values are `n`, `no`, `f`, `false`, `off` and `0`. Raises `ValueError` if val is anything else.

`distutils.util.``byte_compile`(py_files[, optimize=0, force=0, prefix=None, base_dir=None, verbose=1, dry_run=0, direct=None])

  Byte-compile a collection of Python source files to either `.pyc` or `.pyo` files in the same directory. py_files is a list of files to compile; any files that don’t end in `.py` are silently skipped. optimize must be one of the following:

  - `0` - don’t optimize (generate `.pyc`)
  - `1` - normal optimization (like `python -O`)
  - `2` - extra optimization (like `python -OO`)

  If force is true, all files are recompiled regardless of timestamps.

  The source filename encoded in each bytecode file defaults to the filenames listed in py_files; you can modify these with prefix and basedir. prefix is a string that will be stripped off of each source filename, and base_dir is a directory name that will be prepended (after prefix is stripped). You can supply either or both (or neither) of prefix and base_dir, as you wish.

  If dry_run is true, doesn’t actually do anything that would affect the filesystem.

  Byte-compilation is either done directly in this interpreter process with the standard `py_compile` module, or indirectly by writing a temporary script and executing it. Normally, you should let `byte_compile()` figure out to use direct compilation or not (see the source for details). The direct flag is used by the script generated in indirect mode; unless you know what you’re doing, leave it set to `None`.

`distutils.util.``rfc822_escape`(header)
  Return a version of header escaped for inclusion in an RFC 822 header, by ensuring there are 8 spaces space after each newline. Note that it does no other modification of the string.

## 11.14. `distutils.dist` — The Distribution class

This module provides the `Distribution` class, which represents the module distribution being built/installed/distributed.

## 11.15. `distutils.extension` — The Extension class

This module provides the `Extension` class, used to describe C/C++ extension modules in setup scripts.

## 11.16. `distutils.debug` — Distutils debug mode

This module provides the DEBUG flag.

## 11.17. `distutils.errors` — Distutils exceptions

Provides exceptions used by the Distutils modules. Note that Distutils modules may raise standard exceptions; in particular, SystemExit is usually raised for errors that are obviously the end-user’s fault (eg. bad command-line arguments).

This module is safe to use in `from ... import *` mode; it only exports symbols whose names start with `Distutils` and end with `Error`.

## 11.18. `distutils.fancy_getopt` — Wrapper around the standard getopt module

This module provides a wrapper around the standard `getopt` module that provides the following additional features:

- short and long options are tied together
- options have help strings, so `fancy_getopt()` could potentially create a complete usage summary
- options set attributes of a passed-in object
- boolean options can have “negative aliases” — eg. if --quiet is the “negative alias” of --verbose, then --quiet on the command line sets verbose to false.

** Should be replaced with `optik` (which is also now known as `optparse` in Python 2.3 and later). **

`distutils.fancy_getopt.``fancy_getopt`(options, negative_opt, object, args)
  Wrapper function. options is a list of `(long_option, short_option, help_string)` 3-tuples as described in the constructor for `FancyGetopt`. negative_opt should be a dictionary mapping option names to option names, both the key and value should be in the options list. object is an object which will be used to store values (see the `getopt()` method of the `FancyGetopt` class). args is the argument list. Will use `sys.argv[1:]` if you pass `None` as args.

`distutils.fancy_getopt.``wrap_text`(text, width)
  Wraps text to less than width wide.

class `distutils.fancy_getopt.``FancyGetopt`([option_table=None])

  The option_table is a list of 3-tuples: `(long_option, short_option, help_string)`

  If an option takes an argument, its long_option should have `'='` appended; short_option should just be a single character, no `':'` in any case. short_option should be `None` if a long_option doesn’t have a corresponding short_option. All option tuples must have long options.

The `FancyGetopt` class provides the following methods:

`FancyGetopt.``getopt`([args=None, object=None])

  Parse command-line options in args. Store as attributes on object.

  If args is `None` or not supplied, uses `sys.argv[1:]`. If object is `None` or not supplied, creates a new `OptionDummy` instance, stores option values there, and returns a tuple `(args, object)`. If object is supplied, it is modified in place and `getopt()` just returns args; in both cases, the returned args is a modified copy of the passed-in args list, which is left untouched.

`FancyGetopt.``get_option_order`()
  Returns the list of `(option, value)` tuples processed by the previous run of `getopt()` Raises `RuntimeError` if `getopt()` hasn’t been called yet.

`FancyGetopt.``generate_help`([header=None])

  Generate help text (a list of strings, one per suggested line of output) from the option table for this `FancyGetopt` object.

  If supplied, prints the supplied header at the top of the help.

## 11.19. `distutils.filelist` — The FileList class

This module provides the `FileList` class, used for poking about the filesystem and building lists of files.

## 11.20. `distutils.log` — Simple PEP 282-style logging

## 11.21. `distutils.spawn` — Spawn a sub-process

This module provides the `spawn()` function, a front-end to various platform-specific functions for launching another program in a sub-process. Also provides `find_executable()` to search the path for a given executable name.

## 11.22. `distutils.sysconfig` — System configuration information

The `distutils.sysconfig` module provides access to Python’s low-level configuration information. The specific configuration variables available depend heavily on the platform and configuration. The specific variables depend on the build process for the specific version of Python being run; the variables are those found in the `Makefile` and configuration header that are installed with Python on Unix systems. The configuration header is called `pyconfig.h` for Python versions starting with 2.2, and `config.h` for earlier versions of Python.

Some additional functions are provided which perform some useful manipulations for other parts of the `distutils` package.

`distutils.sysconfig.``PREFIX`
  The result of `os.path.normpath(sys.prefix)`.

`distutils.sysconfig.``EXEC_PREFIX`
  The result of `os.path.normpath(sys.exec_prefix)`.

`distutils.sysconfig.``get_config_var`(name)
  Return the value of a single variable. This is equivalent to `get_config_vars().get(name)`.

`distutils.sysconfig.``get_config_vars`(...)
  Return a set of variable definitions. If there are no arguments, this returns a dictionary mapping names of configuration variables to values. If arguments are provided, they should be strings, and the return value will be a sequence giving the associated values. If a given name does not have a corresponding value, `None` will be included for that variable.

`distutils.sysconfig.``get_config_h_filename`()
  Return the full path name of the configuration header. For Unix, this will be the header generated by the configure script; for other platforms the header will have been supplied directly by the Python source distribution. The file is a platform-specific text file.

`distutils.sysconfig.``get_makefile_filename`()
  Return the full path name of the `Makefile` used to build Python. For Unix, this will be a file generated by the configure script; the meaning for other platforms will vary. The file is a platform-specific text file, if it exists. This function is only useful on POSIX platforms.

`distutils.sysconfig.``get_python_inc`([plat_specific[, prefix]])
  Return the directory for either the general or platform-dependent C include files. If plat_specific is true, the platform-dependent include directory is returned; if false or omitted, the platform-independent directory is returned. If prefix is given, it is used as either the prefix instead of `PREFIX`, or as the exec-prefix instead of `EXEC_PREFIX` if plat_specific is true.

`distutils.sysconfig.``get_python_lib`([plat_specific[, standard_lib[, prefix]]])
  Return the directory for either the general or platform-dependent library installation. If plat_specific is true, the platform-dependent include directory is returned; if false or omitted, the platform-independent directory is returned. If prefix is given, it is used as either the prefix instead of `PREFIX`, or as the exec-prefix instead of `EXEC_PREFIX` if plat_specific is true. If standard_lib is true, the directory for the standard library is returned rather than the directory for the installation of third-party extensions.

The following function is only intended for use within the `distutils` package.

`distutils.sysconfig.``customize_compiler`(compiler)

  Do any platform-specific customization of a `distutils.ccompiler.CCompiler` instance.

  This function is only needed on Unix at this time, but should be called consistently to support forward-compatibility. It inserts the information that varies across Unix flavors and is stored in Python’s `Makefile`. This information includes the selected compiler, compiler and linker options, and the extension used by the linker for shared objects.

This function is even more special-purpose, and should only be used from Python’s own build procedures.

`distutils.sysconfig.``set_python_build`()
  Inform the `distutils.sysconfig` module that it is being used as part of the build process for Python. This changes a lot of relative locations for files, allowing them to be located in the build area rather than in an installed Python.

## 11.23. `distutils.text_file` — The TextFile class

This module provides the `TextFile` class, which gives an interface to text files that (optionally) takes care of stripping comments, ignoring blank lines, and joining lines with backslashes.

class `distutils.text_file.``TextFile`([filename=None, file=None, **options])

  This class provides a file-like object that takes care of all the things you commonly want to do when processing a text file that has some line-by-line syntax: strip comments (as long as `#` is your comment character), skip blank lines, join adjacent lines by escaping the newline (ie. backslash at end of line), strip leading and/or trailing whitespace. All of these are optional and independently controllable.

  The class provides a `warn()` method so you can generate warning messages that report physical line number, even if the logical line in question spans multiple physical lines. Also provides `unreadline()` for implementing line-at-a-time lookahead.

  `TextFile` instances are create with either filename, file, or both. `RuntimeError` is raised if both are `None`. filename should be a string, and file a file object (or something that provides `readline()` and `close()` methods). It is recommended that you supply at least filename, so that `TextFile` can include it in warning messages. If file is not supplied, `TextFile` creates its own using the `open()` built-in function.

  The options are all boolean, and affect the values returned by `readline()`

  option name | description | default
  --- | --- | ---
  strip_comments | strip from `'#'` to end-of- line, as well as any whitespace leading up to the `'#'`—unless it is escaped by a backslash | true
  lstrip_ws | strip leading whitespace from each line before returning it | false
  rstrip_ws | strip trailing whitespace (including line terminator!) from each line before returning it. | true
  skip_blanks | skip lines that are empty *after* stripping comments and whitespace. (If both lstrip_ws and rstrip_ws are false, then some lines may consist of solely whitespace: these will *not* be skipped, even if skip_blanks is true.) | true
  join_lines | if a backslash is the last non-newline character on a line after stripping comments and whitespace, join the following line to it to form one logical line; if N consecutive lines end with a backslash, then N+1 physical lines will be joined to form one logical line. | false
  collapse_join | strip leading whitespace from lines that are joined to their predecessor; only matters if `(join_lines and not lstrip_ws)` | false

  Note that since rstrip_ws can strip the trailing newline, the semantics of `readline()` must differ from those of the built-in file object’s `readline()` method! In particular, `readline()` returns `None` for end-of-file: an empty string might just be a blank line (or an all-whitespace line), if rstrip_ws is true but skip_blanks is not.

  `open`(filename)
    Open a new file filename. This overrides any file or filename constructor arguments.
  `close`()
    Close the current file and forget everything we know about it (including the filename and the current line number).
  `warn`(msg[, line=None])
    Print (to stderr) a warning message tied to the current logical line in the current file. If the current logical line in the file spans multiple physical lines, the warning refers to the whole range, such as `"lines 3-5"`. If line is supplied, it overrides the current line number; it may be a list or tuple to indicate a range of physical lines, or an integer for a single physical line.
  `readline`()
    Read and return a single logical line from the current file (or from an internal buffer if lines have previously been “unread” with `unreadline()`). If the join_lines option is true, this may involve reading multiple physical lines concatenated into a single string. Updates the current line number, so calling `warn()` after `readline()` emits a warning about the physical line(s) just read. Returns `None` on end-of-file, since the empty string can occur if rstrip_ws is true but strip_blanks is not.
  `readlines`()
    Read and return the list of all logical lines remaining in the current file. This updates the current line number to the last line of the file.
  `unreadline`(line)
    Push line (a string) onto an internal buffer that will be checked by future `readline()` calls. Handy for implementing a parser with line-at-a-time lookahead. Note that lines that are “unread” with `unreadline()` are not subsequently re-cleansed (whitespace stripped, or whatever) when read with `readline()`. If multiple calls are made to `unreadline()` before a call to `readline()`, the lines will be returned most in most recent first order.

## 11.24. `distutils.version` — Version number classes

## 11.25. `distutils.cmd` — Abstract base class for Distutils commands

This module supplies the abstract base class `Command`.

class `distutils.cmd.``Command`(dist)

  Abstract base class for defining command classes, the “worker bees” of the Distutils. A useful analogy for command classes is to think of them as subroutines with local variables called options. The options are declared in `initialize_options()` and defined (given their final values) in `finalize_options()`, both of which must be defined by every command class. The distinction between the two is necessary because option values might come from the outside world (command line, config file, ...), and any options dependent on other options must be computed after these outside influences have been processed — hence `finalize_options()`. The body of the subroutine, where it does all its work based on the values of its options, is the `run()` method, which must also be implemented by every command class.

  The class constructor takes a single argument dist, a `Distribution` instance.

## 11.26. `distutils.command` — Individual Distutils commands

## 11.27. `distutils.command.bdist` — Build a binary installer

## 11.28. `distutils.command.bdist_packager` — Abstract base class for packagers

## 11.29. `distutils.command.bdist_dumb` — Build a “dumb” installer

## 11.30. `distutils.command.bdist_msi` — Build a Microsoft Installer binary package

class `distutils.command.bdist_msi.``bdist_msi`(Command)

  Builds a Windows Installer (.msi) binary package.

  In most cases, the `bdist_msi` installer is a better choice than the `bdist_wininst` installer, because it provides better support for Win64 platforms, allows administrators to perform non-interactive installations, and allows installation through group policies.

## 11.31. `distutils.command.bdist_rpm` — Build a binary distribution as a Redhat RPM and SRPM

## 11.32. `distutils.command.bdist_wininst` — Build a Windows installer

## 11.33. `distutils.command.sdist` — Build a source distribution

## 11.34. `distutils.command.build` — Build all files of a package

## 11.35. `distutils.command.build_clib` — Build any C libraries in a package

## 11.36. `distutils.command.build_ext` — Build any extensions in a package

## 11.37. `distutils.command.build_py` — Build the .py/.pyc files of a package

## 11.38. `distutils.command.build_scripts` — Build the scripts of a package

## 11.39. `distutils.command.clean` — Clean a package build area

## 11.40. `distutils.command.config` — Perform package configuration

## 11.41. `distutils.command.install` — Install a package

## 11.42. `distutils.command.install_data` — Install data files from a package

## 11.43. `distutils.command.install_headers` — Install C/C++ header files from a package

## 11.44. `distutils.command.install_lib` — Install library files from a package

## 11.45. `distutils.command.install_scripts` — Install script files from a package

## 11.46. `distutils.command.register` — Register a module with the Python Package Index

The `register` command registers the package with the Python Package Index. This is described in more detail in PEP 301.

## 11.47. Creating a new Distutils command

This section outlines the steps to create a new Distutils command.

A new command lives in a module in the `distutils.command` package. There is a sample template in that directory called `command_template`. Copy this file to a new module with the same name as the new command you’re implementing. This module should implement a class with the same name as the module (and the command). So, for instance, to create the command `peel_banana` (so that users can run `setup.py peel_banana`), you’d copy `command_template` to `distutils/command/peel_banana.py`, then edit it so that it’s implementing the class `peel_banana`, a subclass of `distutils.cmd.Command`.

Subclasses of `Command` must define the following methods.

`Command.``initialize_options`()
  Set default values for all the options that this command supports. Note that these defaults may be overridden by other commands, by the setup script, by config files, or by the command-line. Thus, this is not the place to code dependencies between options; generally, `initialize_options()` implementations are just a bunch of `self.foo = None` assignments.

`Command.``finalize_options`()
  Set final values for all the options that this command supports. This is always called as late as possible, ie. after any option assignments from the command-line or from other commands have been done. Thus, this is the place to to code option dependencies: if foo depends on bar, then it is safe to set foo from bar as long as foo still has the same value it was assigned in `initialize_options()`.

`Command.``run`()
  A command’s raison d’etre: carry out the action it exists to perform, controlled by the options initialized in `initialize_options()`, customized by other commands, the setup script, the command-line, and config files, and finalized in `finalize_options()`. All terminal output and filesystem interaction should be done by `run()`.

sub_commands formalizes the notion of a “family” of commands, eg. `install` as the parent with sub-commands `install_lib`, `install_headers`, etc. The parent of a family of commands defines sub_commands as a class attribute; it’s a list of 2-tuples `(command_name, predicate)`, with command_name a string and predicate an unbound method, a string or None. predicate is a method of the parent command that determines whether the corresponding command is applicable in the current situation. (Eg. we `install_headers` is only applicable if we have any C header files to install.) If predicate is None, that command is always applicable.

sub_commands is usually defined at the *end* of a class, because predicates can be unbound methods, so they must already have been defined. The canonical example is the install command.

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