How can I get the path to the %APPDATA% directory in Python?

You may use os.path.expandvars(path):

Return the argument with environment variables expanded. Substrings of the form $name or ${name} are replaced by the value of environment variable name. Malformed variable names and references to non-existing variables are left unchanged.

On Windows, %name% expansions are supported in addition to $name and ${name}.

This comes handy when combining the expanded value with other path components.

Example:

from os import path

sendto_dir = path.expandvars(r'%APPDATA%\Microsoft\Windows\SendTo')
dumps_dir = path.expandvars(r'%LOCALAPPDATA%\CrashDumps')

import os
print os.getenv('APPDATA')