Check the Python source given by C{codeString} for flakes.

    @param codeString: The Python source to check.
    @type codeString: C{str}

    @param filename: The name of the file the source came from, used to report
        errors.
    @type filename: C{str}

    @param reporter: A L{Reporter} instance, where errors and warnings will be
        reported.

    @return: The number of warnings emitted.
    @rtype: C{int}

def check(codeString, filename, reporter=None):
    """
    Check the Python source given by C{codeString} for flakes.

    @param codeString: The Python source to check.
    @type codeString: C{str}

    @param filename: The name of the file the source came from, used to report
        errors.
    @type filename: C{str}

    @param reporter: A L{Reporter} instance, where errors and warnings will be
        reported.

    @return: The number of warnings emitted.
    @rtype: C{int}
    """
    if reporter is None:
        reporter = modReporter._makeDefaultReporter()
    # First, compile into an AST and handle syntax errors.
    try:
        tree = compile(codeString, filename, "exec", _ast.PyCF_ONLY_AST)
    except SyntaxError:
        value = sys.exc_info()[1]
        msg = value.args[0]

        (lineno, offset, text) = value.lineno, value.offset, value.text

        # If there's an encoding problem with the file, the text is None.
        if text is None:
            # Avoid using msg, since for the only known case, it contains a
            # bogus message that claims the encoding the file declared was
            # unknown.
            reporter.unexpectedError(filename, 'problem decoding source')
        else:
            reporter.syntaxError(filename, msg, lineno, offset, text)
        return 1
    except Exception:
        reporter.unexpectedError(filename, 'problem decoding source')
        return 1
    # Okay, it's syntactically valid.  Now check it.
    w = checker.Checker(tree, filename)
    w.messages.sort(key=lambda m: m.lineno)
    for warning in w.messages:
        reporter.flake(warning)
    return len(w.messages)