Question

我使用了Context Manager：cd from this：How do I "cd" in Python?

import os

class cd:
    """Context manager for changing the current working directory"""
    def __init__(self, newPath):
        self.newPath = os.path.expanduser(newPath)

    def __enter__(self):
        self.savedPath = os.getcwd()
        os.chdir(self.newPath)

    def __exit__(self, etype, value, traceback):
        os.chdir(self.savedPath)

实施例

import subprocess # just to call an arbitrary command e.g. 'ls'

# enter the directory like this:
with cd("~/Library"):
   # we are in ~/Library
   subprocess.call("ls")

# outside the context manager we are back wherever we started.

如果我这样使用，为什么不使用此代码：

str = "~/Library"

with cd(str):
   subprocess.call("ls")

错误：

OSError: [Errno 2] No such file or directory: 'cd ~/Library'

Answer 1

您的示例代码似乎可以正常工作。如果我添加＆＃39; cd＆＃39;我只能复制您的错误到str的值，以便它尝试更改为名为＆＃39; cd~ / Library＆＃39;的目录。这也是基于您显示的错误消息而发生的事情。

断

str = "cd ~/Library"
with cd(str):
   subprocess.call("ls")

精细

str = "~/Library"
with cd(str):
   subprocess.call("ls")

如何在Python中将字符串作为变量传递？

1 个答案: