Question

如下文所述守则:

creates an import hook
creates a context manager which sets the meta_path and cleans on exit.
dumps all the imports done by a program passed in input in imports.log

现在,我很想知道,在这种情况下,是否使用环境主管是一个好的想法,因为实际上,我没有标准<条码>/最终的流通,而只是设置和清理。

另一回事——此行:

with CollectorContext(cl, sys.argv,  imports.log ) as cc:

None? 是否应当成为<条码>。

from __future__ import with_statement
import os
import sys

class CollectImports(object):
    """
    Import hook, adds each import request to the loaded set and dumps
    them to file
    """

    def __init__(self):
        self.loaded = set()

    def __str__(self):
        return str(self.loaded)

    def dump_to_file(self, fname):
        """Dump the loaded set to file
        """
        dumped_str =  
 .join(x for x in self.loaded)
        open(fname,  w ).write(dumped_str)

    def find_module(self, module_name, package=None):
        self.loaded.add(module_name)


class CollectorContext(object):
    """Sets the meta_path hook with the passed import hook when
    entering and clean up when exiting
    """

    def __init__(self, collector, argv, output_file):
        self.collector = collector
        self.argv = argv
        self.output_file = output_file

    def __enter__(self):
        self.argv = self.argv[1:]
        sys.meta_path.append(self.collector)

    def __exit__(self, type, value, traceback):
        # TODO: should assert that the variables are None, otherwise
        # we are quitting with some exceptions
        self.collector.dump_to_file(self.output_file)
        sys.meta_path.remove(self.collector)


def main_context():
    cl = CollectImports()

    with CollectorContext(cl, sys.argv,  imports.log ) as cc:
        progname = sys.argv[0]
        code = compile(open(progname).read(), progname,  exec )
        exec(code)


if __name__ ==  __main__ :
    sys.argv = sys.argv[1:]
    main_context()

Answer 1

既然每个人都能顺利工作,我实际上想回去,因为我想把“跑”放在背景经理内部,所以我会说几句话。

此外,现在,我储存了老的雕像,并在撤离时恢复,也许不是根本性的,而是我认为要做的事情。

class CollectorContext(object):
    """Sets the meta_path hook with the passed import hook when
    entering and clean up when exiting
    """

    def __init__(self, collector, argv, output_file):
        self.collector = collector
        self.old_argv = argv[:]
        self.output_file = output_file
        self.progname = self.old_argv[1]

    def __enter__(self):
        sys.argv = self.old_argv[1:]
        sys.meta_path.append(self.collector)
        return self

    def __exit__(self, type, value, traceback):
        # TODO: should assert that the variables are None, otherwise
        # we are quitting with some exceptions
        self.collector.dump_to_file(self.output_file)
        sys.meta_path.remove(self.collector)
        sys.argv = self.old_argv[:]

    def run(self):
        code = compile(open(self.progname).read(), self.progname,  exec )
        exec(code)


def main_context():
    cl = CollectImports()

    with CollectorContext(cl, sys.argv,  imports.log ) as cc:
        cc.run()

Answer 2

我认为这一概念已经过时。同样,我看不出任何理由反对将清理放在<条码>中:条款中,因此背景主管完全适合。

Your cc is None, because you told it to be so.

如果您不希望的话,将 enter__ 返回的方法:




  The value returned by this method is bound to the identifier in the as clause of with statements using this context manager.


def __enter__(self):
    self.argv = self.argv[1:]
    sys.meta_path.append(self.collector)
    return self
    # or
    return self.collector
    # or
    return "I don t know what to return here"


之后

with CollectorContext(cl, sys.argv,  imports.log ) as cc:
    print cc, repr(cc) # there you see what happens.
    progname = sys.argv[0]
    code = compile(open(progname).read(), progname,  exec )
    exec(code)

Answer 3

如果你总是想进行清理,那么你就应当使用一名环境管理员。如果你使用低级特殊方法执行环境主管,我不肯定你使用<代码>try.finally。如果你使用@contextmanager decorator,请以“自然”的方式对背景管理人进行编码,以便你在什么地方使用try.finally,而不是将例外作为参数。

另外,<条码>cc>是您从<条码>>(<>>>> > > /代码>返回的价值。页: 1 我理解环境主管设计的方式是,回报价值是“文字”。情况主管机构做了些什么,并清理了发生其他事情的背景。例如,数据库连接将产生交易,数据库业务在交易范围内进行。

That said, the above is just there to provide maximum flexibility. There s nothing wrong with just creating a context (that manages itself) directly and returning self, or even not returning anything if you don t need to use the context value inside the with. Since you don t use cc anywhere, you could just do and not worry about the return value:

with CollectorContext(cl, sys.argv,  imports.log ):
        progname = sys.argv[0]
        code = compile(open(progname).read(), progname,  exec )
        exec(code)

友情链接