# 32.1 Abstract Grammar

The module defines a string constant `__version__` which is the decimal subversion revision number of the file shown below.

The abstract grammar is currently defined as follows:

    -- ASDL's five builtin types are identifier, int, string, object, bool

    module Python version "$Revision: 43614 $"
    {
    	mod = Module(stmt* body)
    	    | Interactive(stmt* body)
    	    | Expression(expr body)

    	    -- not really an actual node but useful in Jython's typesystem.
    	    | Suite(stmt* body)

    	stmt = FunctionDef(identifier name, arguments args,
                               stmt* body, expr* decorators)
    	      | ClassDef(identifier name, expr* bases, stmt* body)
    	      | Return(expr? value)

    	      | Delete(expr* targets)
    	      | Assign(expr* targets, expr value)
    	      | AugAssign(expr target, operator op, expr value)

    	      -- not sure if bool is allowed, can always use int
     	      | Print(expr? dest, expr* values, bool nl)

    	      -- use 'orelse' because else is a keyword in target languages
    	      | For(expr target, expr iter, stmt* body, stmt* orelse)
    	      | While(expr test, stmt* body, stmt* orelse)
    	      | If(expr test, stmt* body, stmt* orelse)
    	      | With(expr context_expr, expr? optional_vars, stmt* body)

    	      -- 'type' is a bad name
    	      | Raise(expr? type, expr? inst, expr? tback)
    	      | TryExcept(stmt* body, excepthandler* handlers, stmt* orelse)
    	      | TryFinally(stmt* body, stmt* finalbody)
    	      | Assert(expr test, expr? msg)

    	      | Import(alias* names)
    	      | ImportFrom(identifier module, alias* names, int? level)

    	      -- Doesn't capture requirement that locals must be
    	      -- defined if globals is
    	      -- still supports use as a function!
    	      | Exec(expr body, expr? globals, expr? locals)

    	      | Global(identifier* names)
    	      | Expr(expr value)
    	      | Pass | Break | Continue

    	      -- XXX Jython will be different
    	      -- col_offset is the byte offset in the utf8 string the parser uses
    	      attributes (int lineno, int col_offset)

    	      -- BoolOp() can use left & right?
    	expr = BoolOp(boolop op, expr* values)
    	     | BinOp(expr left, operator op, expr right)
    	     | UnaryOp(unaryop op, expr operand)
    	     | Lambda(arguments args, expr body)
    	     | IfExp(expr test, expr body, expr orelse)
    	     | Dict(expr* keys, expr* values)
    	     | ListComp(expr elt, comprehension* generators)
    	     | GeneratorExp(expr elt, comprehension* generators)
    	     -- the grammar constrains where yield expressions can occur
    	     | Yield(expr? value)
    	     -- need sequences for compare to distinguish between
    	     -- x < 4 < 3 and (x < 4) < 3
    	     | Compare(expr left, cmpop* ops, expr* comparators)
    	     | Call(expr func, expr* args, keyword* keywords,
    			 expr? starargs, expr? kwargs)
    	     | Repr(expr value)
    	     | Num(object n) -- a number as a PyObject.
    	     | Str(string s) -- need to specify raw, unicode, etc?
    	     -- other literals? bools?

    	     -- the following expression can appear in assignment context
    	     | Attribute(expr value, identifier attr, expr_context ctx)
    	     | Subscript(expr value, slice slice, expr_context ctx)
    	     | Name(identifier id, expr_context ctx)
    	     | List(expr* elts, expr_context ctx)
    	     | Tuple(expr *elts, expr_context ctx)

    	      -- col_offset is the byte offset in the utf8 string the parser uses
    	      attributes (int lineno, int col_offset)

    	expr_context = Load | Store | Del | AugLoad | AugStore | Param

    	slice = Ellipsis | Slice(expr? lower, expr? upper, expr? step)
    	      | ExtSlice(slice* dims)
    	      | Index(expr value)

    	boolop = And | Or

    	operator = Add | Sub | Mult | Div | Mod | Pow | LShift
                     | RShift | BitOr | BitXor | BitAnd | FloorDiv

    	unaryop = Invert | Not | UAdd | USub

    	cmpop = Eq | NotEq | Lt | LtE | Gt | GtE | Is | IsNot | In | NotIn

    	comprehension = (expr target, expr iter, expr* ifs)

    	-- not sure what to call the first argument for raise and except
    	-- TODO(jhylton): Figure out if there is a better way to handle
    	--                lineno and col_offset fields, particularly when
            --                ast is exposed to Python.
    	excepthandler = (expr? type, expr? name, stmt* body, int lineno,
    	                 int col_offset)

    	arguments = (expr* args, identifier? vararg,
    		     identifier? kwarg, expr* defaults)

            -- keyword arguments supplied to call
            keyword = (identifier arg, expr value)

            -- import name with optional 'as' alias.
            alias = (identifier name, identifier? asname)
    }