rewrite.py 文件源码

def _read_pyc(source, pyc, trace=lambda x: None):
    """Possibly read a pytest pyc containing rewritten code.

    Return rewritten code if successful or None if not.
    """
    try:
        fp = open(pyc, "rb")
    except IOError:
        return None
    with fp:
        try:
            mtime = int(source.mtime())
            size = source.size()
            data = fp.read(12)
        except EnvironmentError as e:
            trace('_read_pyc(%s): EnvironmentError %s' % (source, e))
            return None
        # Check for invalid or out of date pyc file.
        if (len(data) != 12 or data[:4] != imp.get_magic() or
                struct.unpack("<ll", data[4:]) != (mtime, size)):
            trace('_read_pyc(%s): invalid or out of date pyc' % source)
            return None
        try:
            co = marshal.load(fp)
        except Exception as e:
            trace('_read_pyc(%s): marshal.load error %s' % (source, e))
            return None
        if not isinstance(co, types.CodeType):
            trace('_read_pyc(%s): not a code object' % source)
            return None
        return co