一. 兼容
Flask框架兼容与py2和py3版本，来看看是怎么实现的。
二. 代码
Flask框架提供python不同版本的兼容的实现放在flask/_compat.py文件中，如下
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# -*- coding: utf-8 -*-
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 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 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):
class metaclass(type):
def __new__(cls, name, this_bases, d):
return meta(name, bases, d)
return type.__new__(metaclass, 'temporary_class', (), {})
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
三. 解析
Flask框架的py2/py3兼容主要是依赖于six模块，_compat.py文件主要是提供了utf-8编码和字符串格式的兼容，另外还有Ubuntu 14.04对PyPy 2.2.1的支持问题。
- py2的文件需要注明是utf-8编码,py3默认支持utf-8
- py3不再支持iterkeys()，使用iter()将keys()的返回值转换成为一个迭代器
- py2有为非浮点数准备的int和long类型, 在py3里，只有一种整数类型int
具体的py2和py3的语法区别可参考python2 与 python3 语法区别
