def parse_encoding(fp):
    pos = fp.tell()
    fp.seek(0)
    try:
        line1 = fp.readline()
        has_bom = line1.startswith(codecs.BOM_UTF8)
        if has_bom:
            line1 = line1[len(codecs.BOM_UTF8):]

        m = PYTHON_MAGIC_COMMENT_re.match(line1)
        if not m:
            try:
                import parser
                parser.suite(line1)
            except (ImportError, SyntaxError):
                # Either it's a real syntax error, in which case the source is
                # not valid python source, or line2 is a continuation of line1,
                # in which case we don't want to scan line2 for a magic
                # comment.
                pass
            else:
                line2 = fp.readline()
                m = PYTHON_MAGIC_COMMENT_re.match(line2)

        if has_bom:
            if m:
                raise SyntaxError(
                    "python refuses to compile code with both a UTF8 "
                    "byte-order-mark and a magic encoding comment")
            return 'utf_8'
        elif m:
            return m.group(1)
        else:
            return None
    finally:
        fp.seek(pos)
Non recursive DFS to detect cycles
dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/Babel-0.9.6/babel/util.py/parse_encoding--crossover with--dataset/ETHPy150Open mission-liao/pyswagger/pyswagger/utils.py/walk