Equivalent of shell 'cd' command to change the working directory?

You can change the working directory with:

import os

os.chdir(path)

There are two best practices to follow when using this method:

1. Catch the exception (WindowsError, OSError) on invalid path. If the exception is thrown, do not perform any recursive operations, especially destructive ones. They will operate on the old path and not the new one.
2. Return to your old directory when you're done. This can be done in an exception-safe manner by wrapping your chdir call in a context manager, like Brian M. Hunt did in his answer.

Changing the current working directory in a subprocess does not change the current working directory in the parent process. This is true of the Python interpreter as well. You cannot use os.chdir() to change the CWD of the calling process.

Here's an example of a context manager to change the working directory. It is simpler than an ActiveState version referred to elsewhere, but this gets the job done.

Context Manager: cd

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)

Or try the more concise equivalent(below), using ContextManager.

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.

I would use os.chdir like this:

os.chdir("/path/to/change/to")

By the way, if you need to figure out your current path, use os.getcwd().

More here

cd() is easy to write using a generator and a decorator.

from contextlib import contextmanager
import os

@contextmanager
def cd(newdir):
    prevdir = os.getcwd()
    os.chdir(os.path.expanduser(newdir))
    try:
        yield
    finally:
        os.chdir(prevdir)

Then, the directory is reverted even after an exception is thrown:

os.chdir('/home')

with cd('/tmp'):
    # ...
    raise Exception("There's no place like /home.")
# Directory is now back to '/home'.

If you're using a relatively new version of Python, you can also use a context manager, such as this one:

from __future__ import with_statement
from grizzled.os import working_directory

with working_directory(path_to_directory):
    # code in here occurs within the directory

# code here is in the original directory

UPDATE

If you prefer to roll your own:

import os
from contextlib import contextmanager

@contextmanager
def working_directory(directory):
    owd = os.getcwd()
    try:
        os.chdir(directory)
        yield directory
    finally:
        os.chdir(owd)