How to pass string as variable in Python?

Question

I used Context Manager: cd from here: 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)

Example

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.

Why not work this code if I use like this:

str = "~/Library"

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

Error:

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

Try renaming `str` to something that doesn't collide with built-in names. — George Sovetov, Apr 13 '16 at 21:12
Please, reformat your code to indicate that `__enter__` and `__exit__` are methods within class, not just functions. — George Sovetov, Apr 13 '16 at 21:13
Sorry, I missed error message.. I renamed str to cd_path but it still not work — tmsblgh, Apr 13 '16 at 21:16

score 3 · Accepted Answer · answered Apr 13 '16 at 21:27

3

Your example code seems to work as it should. I can only duplicate your error if I added 'cd' to the value of str such that it tried to change to a directory called 'cd ~/Library'. That is also what seems to have happened based on the error message you show.

Broken

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

Fine

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

answered Apr 13 '16 at 21:27

Sam

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You are right, I leave 'cd' right there, I should have copy my own code.. – tmsblgh Apr 14 '16 at 06:10

How to pass string as variable in Python?

1 Answers1