python之six用法

six.PY2 返回一个表示当前运行环境是否为python2的boolean值

six.PY3 返回一个表示当前运行环境是否为python3的boolean值

import six,sys

print(six.PY2)    #python2结果为True
print(six.PY3)    #python3结果为True

sys.version_info[0]    #PY2 = 2
sys.version_info[0]    #PY3 = 3
sys.version_info[0:2]  #PY34>= (3, 4)

常量

• six.class_types

这里主要是针对python中的old-style和new-style, new-style为type, old-style为 types.ClassType。

python2中同时有old-style和new-style，python3中只有new-style。

• six.integer_types

这里针对python2和python3中各自支持的int类型进行了区分：在python2中，存在 int 和 long 两种整数类型；在python3中，仅存在一种类型int。

• six.string_types

这里针对python2和python3中各自的string类型进行了区分：在python2中，使用的为basestring；在python3中，使用的为str。

• six.text_type

这里针对python2和python3中的文本字符进行了区分：在python2中，使用的文本字符的类型为unicode；在python3中使用的文本字符的类型为str。

具体可以参考Python2 与 Python3 的编码对比

• six.MAXSIZE

list、string、dict以及其他的容器所能支持的最大尺寸。

if PY3:
    string_types = str,
    integer_types = int,
    class_types = type,
    text_type = str
    binary_type = bytes

    MAXSIZE = sys.maxsize
else:
    string_types = basestring,
    integer_types = (int, long)
    class_types = (type, types.ClassType)
    text_type = unicode
    binary_type = str

    if sys.platform.startswith("java"):
        # Jython always uses 32 bits.
        MAXSIZE = int((1 << 31) - 1)
    else:
        # It's possible to have sizeof(long) != sizeof(Py_ssize_t).
        class X(object):

            def __len__(self):
                return 1 << 31
        try:
            len(X())
        except OverflowError:
            # 32-bit
            MAXSIZE = int((1 << 31) - 1)
        else:
            # 64-bit
            MAXSIZE = int((1 << 63) - 1)
        del X

对象模型兼容

• six.get_unbound_function(meth)

针对python2和python3中unbound function的支持不同，在python2中存在unbound function，在python3中不存在unbound function。

if PY3:
    def get_unbound_function(unbound):
        return unbound
else:
    def get_unbound_function(unbound):
        return unbound.im_func

有关的测试代码如下:

>>> class Foo():
...     def bar():
...             print(1)
...     def too(self):
...             print(2)
...
>>>

在python2的环境中：

>>> Foo.bar
<unbound method Foo.bar>
>>> Foo().bar
<bound method Foo.bar of <__main__.Foo instance at 0x10e8a7998>>
>>> Foo.too
<unbound method Foo.too>
>>> Foo().too
<bound method Foo.too of <__main__.Foo instance at 0x10e8a7998>>

在python3的环境中：

>>> Foo.bar
<function Foo.bar at 0x10ebe4bf8>
>>> Foo().bar
<bound method Foo.bar of <__main__.Foo object at 0x10ebeaa58>>
>>> Foo.too
<function Foo.too at 0x10ebe4c80>
>>> Foo().bar
<bound method Foo.bar of <__main__.Foo object at 0x10ebeaa58>>

使用six.get_unbound_function(meth)：

在python2环境中：

>>> import six
>>> six.get_unbound_function(Foo.too)
<function too at 0x10e89faa0>
>>> six.get_unbound_function(Foo.bar)
<function bar at 0x10e89fa28>

在python3环境中：

>>> import six
>>> six.get_unbound_function(Foo.too)
<function Foo.too at 0x10a158c80>
>>> six.get_unbound_function(Foo.bar)
<function Foo.bar at 0x10a158bf8>

• six.get_method_function(meth)

此方法可以在方法对象之外得到函数。在python2中使用im_func, 在python3中使用__func__。

if PY3:
    _meth_func = "__func__"
else:
    _meth_func = "im_func"
get_method_function = operator.attrgetter(_meth_func)

有关的测试代码如下:

>>> class Foo():
...     def bar():
...             print(1)
...     def too(self):
...             print(2)
...
>>>

在python2环境中：

>>> import six
>>> six.get_method_function(Foo().bar)
<function bar at 0x10c8c6a28>
>>> six.get_method_function(Foo.bar)
<function bar at 0x10c8c6a28>
>>> six.get_method_function(Foo().too)
<function too at 0x10c8c6aa0>
>>> six.get_method_function(Foo.too)
<function too at 0x10c8c6aa0>

在python3环境中：

>>> import six
>>> six.get_method_function(Foo.bar)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute '__func__'
>>> six.get_method_function(Foo().bar)
<function Foo.bar at 0x1047dbbf8>
>>> six.get_method_function(Foo.too)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute '__func__'
>>> six.get_method_function(Foo().too)
<function Foo.too at 0x1047dbc80>

• six.get_method_self(meth)

针对python2以及python3中的不同，返回bound method的self。其中：python2中使用im_self，python3中使用__self__。

if PY3:
    _meth_self = "__self__"
else:
    _meth_self = "im_self"
get_method_self = operator.attrgetter(_meth_self)

有关的测试代码如下:

>>> class Foo():
...     def bar():
...             print(1)
...     def too(self):
...             print(2)
...
>>>

在python2的环境中：

>>> import six
>>> six.get_method_self(Foo.bar)
>>> a = six.get_method_self(Foo.bar)
>>> a
>>> six.get_method_self(Foo().bar)
<__main__.Foo instance at 0x10563da70>
>>> a = six.get_method_self(Foo().bar)
>>> a
<__main__.Foo instance at 0x10563dd88>
>>> six.get_method_self(Foo.too)
>>> a = six.get_method_self(Foo.too)
>>> a
>>> six.get_method_self(Foo().too)
<__main__.Foo instance at 0x10563da28>
>>> a = six.get_method_self(Foo().too)
>>> a
<__main__.Foo instance at 0x10563da70>

在python3的环境中：

>>> import six
>>> six.get_method_self(Foo.bar)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute '__self__'
>>> six.get_method_self(Foo().bar)
<__main__.Foo object at 0x1059bbb00>
>>> six.get_method_self(Foo.too)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute '__self__'
>>> six.get_method_self(Foo().too)
<__main__.Foo object at 0x1059bbb38>

• six.get_function_closure(func)

针对python2和python3中的不同，返回函数当中的闭包。其中，python2使用func_closure，python3使用 __closure__。

if PY3:
    _func_closure = "__closure__"
else:
    _func_closure = "func_closure"

get_function_closure = operator.attrgetter(_func_closure)

关于闭包的理解可以参考:

1. 浅显理解 Python 闭包
2. 闭包的概念、形式与应用

有关的测试代码如下：

>>> def foo(n):
...     a = 1
...     def bar(n):
...             return a-n
...     return bar

此处需要注意的是foo函数返回的是bar函数，而不是具体的值。

在python2的环境当中：

>>> foo.__closure__
>>> foo(1)
<function bar at 0x10c25aa28>
>>> foo(1).__closure__
(<cell at 0x10c25eb40: int object at 0x7f9460d0bca8>,)
>>> foo(1).func_closure
(<cell at 0x10c25ed70: int object at 0x7f9460d0bca8>,)

在python3的环境当中：

>>> foo.__closure__
>>> foo(1)
<function foo.<locals>.bar at 0x10c46dbf8>
>>> foo(1).__closure__
(<cell at 0x10c451198: int object at 0x10be73170>,)
>>> foo(1).func_closure
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute 'func_closure'

• six.get_function_code(func)

针对python2和python3中获取func中的code对象，将使用不同的方式进行获取。在python2中，将使用func_code；在python3中，将使用code。

if PY3:
    _func_code = "__code__"
else:
    _func_code = "func_code"
get_function_code = operator.attrgetter(_func_code)

如果你对其中的code object是什么比较感兴趣，可以参考下面的资料：

1. Exploring Python Code Objects

有关的测试代码如下：

>>> def boo():
...     return 1

在python2的环境当中：

>>> boo.func_code
<code object boo at 0x1101092b0, file "<stdin>", line 1>
>>> boo().func_code
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'func_code'

在python3的环境当中：

>>> boo.__code__
<code object boo at 0x104d8a930, file "<stdin>", line 1>
>>> boo().__code__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute '__code__'

• six.get_function_defaults(func)

针对python2和python3中的区别，获取func中的默认元组。在python2中，使用func_defaults；在python3中，使用__defaults__。

if PY3:
    _func_defaults = "__defaults__"
else:
    _func_defaults = "func_defaults"
get_function_defaults = operator.attrgetter(_func_defaults)

有关的测试代码如下:

>>> def boo(a=1):
...     return a
...

在python2环境中：

>>> boo.func_defaults
(1,)
>>> boo.__defaults__
(1,)
>>> boo().func_defaults
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'func_defaults'
>>> boo().__defaults__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute '__defaults__'

在python3环境中:

>>> boo.__defaults__
(1,)
>>> boo.func_defaults
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute 'func_defaults'
>>> boo().__defaults__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute '__defaults__'
>>> boo().func_defaults
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'func_defaults'

• six.get_function_globals(func)

获取函数当中的全局变量。在python2中，使用func_globals；在python3中，使用__globals__。

if PY3:
    _func_globals = "__globals__"
else:
    _func_globals = "func_globals"
get_function_globals = operator.attrgetter(_func_globals)

有关的测试代码：

>>> def boo(a=1):
...     x = 100
...     b = x - a
...     return b

在python2环境中:

>>> boo.__globals__
{'__builtins__': <module '__builtin__' (built-in)>, '__name__': '__main__', 'boo': <function boo at 0x109a6e9b0>, '__doc__': None, '__package__': None}
>>> boo.func_globals
{'__builtins__': <module '__builtin__' (built-in)>, '__name__': '__main__', 'boo': <function boo at 0x109a6e9b0>, '__doc__': None, '__package__': None}

在python3环境中:

>>> boo.__globals__
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'boo': <function boo at 0x1029d8e18>}
>>> boo.func_globals
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute 'func_globals'

• six.next(it) or six.advance_iterator(it)

获取到迭代器的下一个。在python2环境中，使用it.next()；在python3环境中，使用next(it)

try:
    advance_iterator = next
except NameError:
    def advance_iterator(it):
        return it.next()
next = advance_iterator

关于迭代器的内容可以参考一下文件：

1. 迭代器

在python2环境中：

>>> it = iter([1,2,3,4,5])
>>> while True:
...     try:
...             x = it.next()
...     except NameError:
...             print "name error"
...     except StopIteration:
...             print "end"
...             break
...
end

>>> it = iter([1,2,3,4,5])
>>> while True:
...     try:
...             x = next(it)
...     except NameError:
...             print "name error"
...     except StopIteration:
...             print "end"
...             break
...
end

在python3环境中：

>>> it = iter([1,2,3,4,5])
>>> while True:
...     try:
...             x = it.next()
...     except NameError:
...             print("name error")
...     except StopIteration:
...             print("end")
...             break
...
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
AttributeError: 'list_iterator' object has no attribute 'next'

>>> it = iter([1,2,3,4,5])
>>> while True:
...     try:
...             x = next(it)
...     except NameError:
...             print("name error")
...     except StopIteration:
...             print("end")
...             break
...
end

• six.callable(obj)

该方法用来检验obj是否可以进行调用。

关于python的callable属性，请参考一下文件：

try:
    callable = callable
except NameError:
    def callable(obj):
        return any("__call__" in klass.__dict__ for klass in type(obj).__mro__)

有关的测试代码：

>>> def add(x, y):
...     return x + y
...

在python2环境中：

>>> callable(add)
True

在python 3.1环境中：

>>> callable(add)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'callable' is not defined

在python3.2之后的环境中：

>>> callable(add)
True