Flask源码阅读-第三篇(flask\_compat.py)

源码

# -*- 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 by the Pallets team.
    :license: BSD, see LICENSE for more details.
"""

import sys

PY2 = sys.version_info[0] == 2
_identity = lambda x: x

if not PY2:
    text_type = str
    string_types = (str,)
    integer_types = (int,)

    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

    def reraise(tp, value, tb=None):
        if value.__traceback__ is not tb:
            raise value.with_traceback(tb)
        raise value

    implements_to_string = _identity

else:
    text_type = unicode
    string_types = (str, unicode)
    integer_types = (int, long)

    iterkeys = lambda d: d.iterkeys()
    itervalues = lambda d: d.itervalues()
    iteritems = lambda d: d.iteritems()

    from inspect import getargspec
    from cStringIO import StringIO

    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__(cls, 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:
            raise
    except TypeError:
        BROKEN_PYPY_CTXMGR_EXIT = True
    except AssertionError:
        pass

解读

本模块主要是做了些兼容处理，主要从python2与其他版本进行比较。从这可以看出python2在编码等方面是有一定差异的，我们了解即可，以下一些关键语句就是对这种差异做兼容处理：

   text_type = unicode
   string_types = (str, unicode)

   integer_types = (int, long)

   cls.__str__ = lambda x: x.__unicode__().encode('utf-8')