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Filename : example.py
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"""Simple code to extract class & function docstrings from a module.

This code is used as an example in the library reference manual in the
section on using the parser module.  Refer to the manual for a thorough
discussion of the operation of this code.
"""

import os
import parser
import symbol
import token
import types

from types import ListType, TupleType


def get_docs(fileName):
    """Retrieve information from the parse tree of a source file.

    fileName
        Name of the file to read Python source code from.
    """
    source = open(fileName).read()
    basename = os.path.basename(os.path.splitext(fileName)[0])
    ast = parser.suite(source)
    return ModuleInfo(ast.totuple(), basename)


class SuiteInfoBase:
    _docstring = ''
    _name = ''

    def __init__(self, tree = None):
        self._class_info = {}
        self._function_info = {}
        if tree:
            self._extract_info(tree)

    def _extract_info(self, tree):
        # extract docstring
        if len(tree) == 2:
            found, vars = match(DOCSTRING_STMT_PATTERN[1], tree[1])
        else:
            found, vars = match(DOCSTRING_STMT_PATTERN, tree[3])
        if found:
            self._docstring = eval(vars['docstring'])
        # discover inner definitions
        for node in tree[1:]:
            found, vars = match(COMPOUND_STMT_PATTERN, node)
            if found:
                cstmt = vars['compound']
                if cstmt[0] == symbol.funcdef:
                    name = cstmt[2][1]
                    self._function_info[name] = FunctionInfo(cstmt)
                elif cstmt[0] == symbol.classdef:
                    name = cstmt[2][1]
                    self._class_info[name] = ClassInfo(cstmt)

    def get_docstring(self):
        return self._docstring

    def get_name(self):
        return self._name

    def get_class_names(self):
        return self._class_info.keys()

    def get_class_info(self, name):
        return self._class_info[name]

    def __getitem__(self, name):
        try:
            return self._class_info[name]
        except KeyError:
            return self._function_info[name]


class SuiteFuncInfo:
    #  Mixin class providing access to function names and info.

    def get_function_names(self):
        return self._function_info.keys()

    def get_function_info(self, name):
        return self._function_info[name]


class FunctionInfo(SuiteInfoBase, SuiteFuncInfo):
    def __init__(self, tree = None):
        self._name = tree[2][1]
        SuiteInfoBase.__init__(self, tree and tree[-1] or None)


class ClassInfo(SuiteInfoBase):
    def __init__(self, tree = None):
        self._name = tree[2][1]
        SuiteInfoBase.__init__(self, tree and tree[-1] or None)

    def get_method_names(self):
        return self._function_info.keys()

    def get_method_info(self, name):
        return self._function_info[name]


class ModuleInfo(SuiteInfoBase, SuiteFuncInfo):
    def __init__(self, tree = None, name = "<string>"):
        self._name = name
        SuiteInfoBase.__init__(self, tree)
        if tree:
            found, vars = match(DOCSTRING_STMT_PATTERN, tree[1])
            if found:
                self._docstring = vars["docstring"]


def match(pattern, data, vars=None):
    """Match `data' to `pattern', with variable extraction.

    pattern
        Pattern to match against, possibly containing variables.

    data
        Data to be checked and against which variables are extracted.

    vars
        Dictionary of variables which have already been found.  If not
        provided, an empty dictionary is created.

    The `pattern' value may contain variables of the form ['varname'] which
    are allowed to match anything.  The value that is matched is returned as
    part of a dictionary which maps 'varname' to the matched value.  'varname'
    is not required to be a string object, but using strings makes patterns
    and the code which uses them more readable.

    This function returns two values: a boolean indicating whether a match
    was found and a dictionary mapping variable names to their associated
    values.
    """
    if vars is None:
        vars = {}
    if type(pattern) is ListType:       # 'variables' are ['varname']
        vars[pattern[0]] = data
        return 1, vars
    if type(pattern) is not TupleType:
        return (pattern == data), vars
    if len(data) != len(pattern):
        return 0, vars
    for pattern, data in map(None, pattern, data):
        same, vars = match(pattern, data, vars)
        if not same:
            break
    return same, vars


#  This pattern identifies compound statements, allowing them to be readily
#  differentiated from simple statements.
#
COMPOUND_STMT_PATTERN = (
    symbol.stmt,
    (symbol.compound_stmt, ['compound'])
    )


#  This pattern will match a 'stmt' node which *might* represent a docstring;
#  docstrings require that the statement which provides the docstring be the
#  first statement in the class or function, which this pattern does not check.
#
DOCSTRING_STMT_PATTERN = (
    symbol.stmt,
    (symbol.simple_stmt,
     (symbol.small_stmt,
      (symbol.expr_stmt,
       (symbol.testlist,
        (symbol.test,
         (symbol.and_test,
          (symbol.not_test,
           (symbol.comparison,
            (symbol.expr,
             (symbol.xor_expr,
              (symbol.and_expr,
               (symbol.shift_expr,
                (symbol.arith_expr,
                 (symbol.term,
                  (symbol.factor,
                   (symbol.power,
                    (symbol.atom,
                     (token.STRING, ['docstring'])
                     )))))))))))))))),
     (token.NEWLINE, '')
     ))