src/_compat.py
_compat.py
Official Document
Some py2/py3 compatibility support based on a stripped down version of six so we don’t have to depend on a specific version of it.
Overview
This is a simple module which shares some concepts from the Python library six to support both Python 2 code and Python 3 code.
Details
Python Version
At first, the current Python version is obtained and then the code decides what to include in this module.
import sys
PY2 = sys.version_info[0] == 2
Simple Code
The code below shows some basic interfaces, and they are about strings, iterations and so on. Note that the purpose is just to adapt Python 2 code and Python 3 code, and there is nothing special here.
_identity = lambda x: x
try: # Python 2
text_type = unicode
string_types = (str, unicode)
integer_types = (int, long)
except NameError: # Python 3
text_type = str
string_types = (str,)
integer_types = (int,)
if not PY2:
iterkeys = lambda d: iter(d.keys())
itervalues = lambda d: iter(d.values())
iteritems = lambda d: iter(d.items())
from inspect import getfullargspec as getargspec
from io import StringIO
import collections.abc as collections_abc
def reraise(tp, value, tb=None):
if value.__traceback__ is not tb:
raise value.with_traceback(tb)
raise value
implements_to_string = _identity
else:
iterkeys = lambda d: d.iterkeys()
itervalues = lambda d: d.itervalues()
iteritems = lambda d: d.iteritems()
from inspect import getargspec
from cStringIO import StringIO
import collections as collections_abc
exec("def reraise(tp, value, tb=None):\n raise tp, value, tb")
def implements_to_string(cls):
cls.__unicode__ = cls.__str__
cls.__str__ = lambda x: x.__unicode__().encode("utf-8")
return cls
with_metaclass
Note that this is an advanced concept of metaclasses, and 99% of programmers never use it. Simply speaking, this method is used to utilize metaclass in both Python 2 and Python 3, and a detailed discussion on stackoverflow.com is here.
def with_metaclass(meta, *bases):
"""Create a base class with a metaclass."""
class metaclass(type):
def __new__(metacls, name, this_bases, d):
return meta(name, bases, d)
return type.__new__(metaclass, "temporary_class", (), {})
fspath
The method fspath returns the file system representation of the path, and there is nothing special here.
try:
from os import fspath
except ImportError:
def fspath(path):
return path.__fspath__() if hasattr(path, "__fspath__") else path
pypy Bug Fix
In the middle of _compat.py, some code about pypy is represented. I will ignore this code until I start to use pypy.
Source Code
# -*- coding: utf-8 -*-
"""
flask._compat
~~~~~~~~~~~~~
Some py2/py3 compatibility support based on a stripped down
version of six so we don't have to depend on a specific version
of it.
:copyright: 2010 Pallets
:license: BSD-3-Clause
"""
import sys
PY2 = sys.version_info[0] == 2
_identity = lambda x: x
try: # Python 2
text_type = unicode
string_types = (str, unicode)
integer_types = (int, long)
except NameError: # Python 3
text_type = str
string_types = (str,)
integer_types = (int,)
if not PY2:
iterkeys = lambda d: iter(d.keys())
itervalues = lambda d: iter(d.values())
iteritems = lambda d: iter(d.items())
from inspect import getfullargspec as getargspec
from io import StringIO
import collections.abc as collections_abc
def reraise(tp, value, tb=None):
if value.__traceback__ is not tb:
raise value.with_traceback(tb)
raise value
implements_to_string = _identity
else:
iterkeys = lambda d: d.iterkeys()
itervalues = lambda d: d.itervalues()
iteritems = lambda d: d.iteritems()
from inspect import getargspec
from cStringIO import StringIO
import collections as collections_abc
exec("def reraise(tp, value, tb=None):\n raise tp, value, tb")
def implements_to_string(cls):
cls.__unicode__ = cls.__str__
cls.__str__ = lambda x: x.__unicode__().encode("utf-8")
return cls
def with_metaclass(meta, *bases):
"""Create a base class with a metaclass."""
# This requires a bit of explanation: the basic idea is to make a
# dummy metaclass for one level of class instantiation that replaces
# itself with the actual metaclass.
class metaclass(type):
def __new__(metacls, name, this_bases, d):
return meta(name, bases, d)
return type.__new__(metaclass, "temporary_class", (), {})
# Certain versions of pypy have a bug where clearing the exception stack
# breaks the __exit__ function in a very peculiar way. The second level of
# exception blocks is necessary because pypy seems to forget to check if an
# exception happened until the next bytecode instruction?
#
# Relevant PyPy bugfix commit:
# https://bitbucket.org/pypy/pypy/commits/77ecf91c635a287e88e60d8ddb0f4e9df4003301
# According to ronan on #pypy IRC, it is released in PyPy2 2.3 and later
# versions.
#
# Ubuntu 14.04 has PyPy 2.2.1, which does exhibit this bug.
BROKEN_PYPY_CTXMGR_EXIT = False
if hasattr(sys, "pypy_version_info"):
class _Mgr(object):
def __enter__(self):
return self
def __exit__(self, *args):
if hasattr(sys, "exc_clear"):
# Python 3 (PyPy3) doesn't have exc_clear
sys.exc_clear()
try:
try:
with _Mgr():
raise AssertionError()
except: # noqa: B001
# We intentionally use a bare except here. See the comment above
# regarding a pypy bug as to why.
raise
except TypeError:
BROKEN_PYPY_CTXMGR_EXIT = True
except AssertionError:
pass
try:
from os import fspath
except ImportError:
# Backwards compatibility as proposed in PEP 0519:
# https://www.python.org/dev/peps/pep-0519/#backwards-compatibility
def fspath(path):
return path.__fspath__() if hasattr(path, "__fspath__") else path