[python] Telling Python to save a .txt file to a certain directory on Windows and Mac

Use os.path.join to combine the path to the Documents directory with the completeName (filename?) supplied by the user.

import os
with open(os.path.join('/path/to/Documents',completeName), "w") as file1:
    toFile = raw_input("Write what you want into the field")
    file1.write(toFile)

If you want the Documents directory to be relative to the user's home directory, you could use something like:

os.path.join(os.path.expanduser('~'),'Documents',completeName)

Others have proposed using os.path.abspath. Note that os.path.abspath does not resolve '~' to the user's home directory:

In [10]: cd /tmp
/tmp

In [11]: os.path.abspath("~")
Out[11]: '/tmp/~'