Problems with umlauts in python appdata environvent variable

Question

I can't find a correct way to get the environment variable for the appdata path in python.

The problem is that my user name includes special characters (the german ae and ue). I made a workaround wit PyQt for Vista and Windows 7 but it doesn't work for XP Systems.

Does anybody know the correct encoding of these environment variables or another solution for this problem?

Answer 1

As Mike says, you can get the system codepage from getfilesystemencoding. This encoding is used to convert Windows's native Unicode strings into bytes for all C stdio functions used by Python, including the filesystem calls that use byte string filepaths, and os.environ.

What this means is that you will be able to read a string with non-ASCII characters from os.environ and use it directly as a filepath without any special encode/decode step.

Unfortunately, if the %APPDATA% variable contains Unicode characters that are not present in the system codepage — for example, if on a German (cp1252) Windows install, your path was C:\Documents and Settings\αβγ\Application Data — then those characters will have already been mangled before you get the chance to use them. Decoding the byte string you get to Unicode using the filesystemencoding won't help in that case.

Here's a function you can use on recent Python versions that have the ctypes extension, to read Windows native Unicode environment variables.

def getEnvironmentVariable(name):
    name= unicode(name) # make sure string argument is unicode
    n= ctypes.windll.kernel32.GetEnvironmentVariableW(name, None, 0)
    if n==0:
        return None
    buf= ctypes.create_unicode_buffer(u'\0'*n)
    ctypes.windll.kernel32.GetEnvironmentVariableW(name, buf, n)
    return buf.value

In Python 3, the os.environ dictionary contains Unicode strings taken directly from Windows with no codepage encoding, so you don't have to worry about this problem there.