我最近一直想知道是否有办法检测上下文管理器是否嵌套.

我创建了Timer和TimerGroup类：

class Timer:
    def __init__(self, name="Timer"):
        self.name = name
        self.start_time = clock()

    @staticmethod
    def seconds_to_str(t):
        return str(timedelta(seconds=t))

    def end(self):
        return clock() - self.start_time

    def print(self, t):
        print(("{0:<" + str(line_width - 18) + "} >> {1}").format(self.name, self.seconds_to_str(t)))

    def __enter__(self):
        return self

    def __exit__(self, exc_type, value, traceback):
        self.print(self.end())


class TimerGroup(Timer):
    def __enter__(self):
        print(('= ' + self.name + ' ').ljust(line_width, '='))
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        total_time = self.seconds_to_str(self.end())
        print(" Total: {0}".format(total_time).rjust(line_width, '='))
        print()

此代码以可读格式打印时序：

with TimerGroup("Collecting child documents for %s context" % context_name):
    with Timer("Collecting context features"):
        # some code...
    with Timer("Collecting child documents"):
        # some code...


= Collecting child documents for Global context ============
Collecting context features                >> 0:00:00.001063
Collecting child documents                 >> 0:00:10.611130
====================================== Total: 0:00:10.612292

但是,当我嵌套TimerGroups时,它搞砸了：

with TimerGroup("Choosing the best classifier for %s context" % context_name):
    with Timer("Splitting datasets"):
        # some code...
    for cname, cparams in classifiers.items():
        with TimerGroup("%s classifier" % cname):
            with Timer("Training"):
                # some code...
            with Timer("Calculating accuracy on testing set"):
                # some code


= Choosing the best classifier for Global context ==========
Splitting datasets                         >> 0:00:00.002054
= Naive Bayes classifier ===================================
Training                                   >> 0:00:34.184903
Calculating accuracy on testing set        >> 0:05:08.481904
====================================== Total: 0:05:42.666949

====================================== Total: 0:05:42.669078

我需要做的就是以某种方式缩进嵌套的Timers和TimerGroups.我应该将任何参数传递给他们的构造函数吗？或者我可以从班级内部发现吗？

解决方法:

如果您需要做的就是根据您正在执行的嵌套上下文管理器的数量来调整缩进级别,那么请使用名为indent_level的类属性,并在每次进入和退出上下文管理器时对其进行调整.类似于以下内容：

class Context:
    indent_level = 0

    def __init__(self, name):
        self.name = name

    def __enter__(self):
        print(' '*4*self.indent_level + 'Entering ' + self.name)
        self.adjust_indent_level(1)
        return self

    def __exit__(self, *a, **k):
        self.adjust_indent_level(-1)
        print(' '*4*self.indent_level + 'Exiting ' + self.name)

    @classmethod
    def adjust_indent_level(cls, val):
        cls.indent_level += val

并将其用作：

>>> with Context('Outer') as outer_context:
        with Context('Inner') as inner_context:
            print(' '*inner_context.indent_level*4 + 'In the inner context')


Entering Outer
    Entering Inner
        In the inner context
    Exiting Inner
Exiting Outer