上下文管理员是否适合这份工作？

Question

下面粘贴的代码执行以下操作:

• 创建一个导入钩子
• 创建一个上下文管理器,用于设置meta_path和清除退出.
• 转储在imports.log中输入的程序完成的所有导入

现在我想知道在这种情况下使用上下文管理器是否是一个好主意,因为实际上我没有标准try/finally流程,只是设置和清理.

另一件事 - 用这条线:

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

确实cc成了None？它不应该是一个CollectorContext对象吗？

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 = '\n'.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

谢谢大家，现在它工作顺利，我实际上想要返回一些东西，因为我想将“运行”封装在上下文管理器中，所以我得到如下所示的东西。

此外，现在我存储旧的 sys.argv 并在退出时恢复它，可能不是根本性的，但我认为仍然是一件好事。

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()