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# autoreload

`autoreload` is an IPython extension that reloads modules automatically before executing the line of code typed.

This makes for example the following workflow possible:

    In [1]: %load_ext autoreload

    In [2]: %autoreload 2

    In [3]: from foo import some_function

    In [4]: some_function()
    Out[4]: 42

    In [5]: # open foo.py in an editor and change some_function to return 43

    In [6]: some_function()
    Out[6]: 43

The module was reloaded without reloading it explicitly, and the object imported with `from foo import ...` was also updated.

## Usage

The following magic commands are provided:

`%autoreload`

> Reload all modules (except those excluded by `%aimport`) automatically now.

`%autoreload 0`

> Disable automatic reloading.

`%autoreload 1`

> Reload all modules imported with `%aimport` every time before executing the Python code typed.

`%autoreload 2`

> Reload all modules (except those excluded by `%aimport`) every time before executing the Python code typed.

`%aimport`

> List modules which are to be automatically imported or not to be imported.

`%aimport foo`

> Import module ‘foo’ and mark it to be autoreloaded for `%autoreload 1`

`%aimport -foo`

> Mark module ‘foo’ to not be autoreloaded.

## Caveats

Reloading Python modules in a reliable way is in general difficult, and unexpected things may occur. `%autoreload` tries to work around common pitfalls by replacing function code objects and parts of classes previously in the module with new versions. This makes the following things to work:

- Functions and classes imported via ‘from xxx import foo’ are upgraded to new versions when ‘xxx’ is reloaded.
- Methods and properties of classes are upgraded on reload, so that calling ‘c.foo()’ on an object ‘c’ created before the reload causes the new code for ‘foo’ to be executed.

Some of the known remaining caveats are:

- Replacing code objects does not always succeed: changing a @property in a class to an ordinary method or a method to a member variable can cause problems (but in old objects only).
- Functions that are removed (eg. via monkey-patching) from a module before it is reloaded are not upgraded.
- C extension modules cannot be reloaded, and so cannot be autoreloaded.

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