contexter 0.1.4

Contexter是contextlib [1]标准库模块的全替代品。它包含更多功能，更好的API，并从单个源文件支持Python 2.5到3.x的全版本。

简而言之：Contexter允许您以简单直观的方式嵌套和堆叠上下文管理器。

不多说了，让我们看看一个例子

''' Copy the content of one file to another
     and protect everything with a lock. '''

with Contexter(lock) as ctx:
    in_file  = ctx << open('a.txt')
    out_file = ctx << open('b.txt', 'w')
    out_file.write(in_file.read())

看看这个。它很漂亮，不是吗？让我来解释一下：您可以使用任意数量的上下文管理器作为参数调用Contexter()，然后使用简洁的value = ctx << thing语法附加额外的管理器。就这样。只需一个缩进级别，无论您需要多少个管理器。

仅作比较

# Python 2.5 and 2.6
with lock:
    with open('a.txt') as in_file:
        with open('b.txt', 'w') as out_file:
            out_file.write(in_file.read())

# Starting with Python 2.7 and 3.2
with lock, open('a.txt') as in_file, open('b.txt', 'w') as out_file:
    out_file.write(in_file.read())

# Deprecated since Python 2.7 and 3.2
with contextlib.nested(lock, open('a.txt'), open('b.txt', 'w')) as values:
    in_file, out_file = values
    out_file.write(in_file.read())

# Since Python 3.3 (not backported to 2.7)
with contextlib.ExitStack() as stack:
    stack.enter_context(lock)
    in_file  = stack.enter_context(open('a.txt'))
    out_file = stack.enter_context(open('b.txt', 'w'))
    out_file.write(in_file.read())

with Contexter(open('a.txt'), open('b.txt', 'w')) as ctx:
    in_file, out_file = ctx.values()
    assert ctx.value(0) is in_file
    assert ctx[0] is in_file
    assert ctx[0:2] == [in_file, out_file]
    assert len(ctx) == 2

with Contexter() as ctx:
    in_file = ctx << open('a.txt')
    out_file = ctx.append(open('b.txt', 'w'))

with Contexter() as ctx:
    out_file = ctx << open('b.txt', 'w')

    with ctx:
        in_file = ctx << open('a.txt')
        copy_data(in_file, out_file)

    assert in_file.closed == True
    assert out_file.closed == False