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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def guess_project_dir():
 """Find the top-level Django project directory. This function guesses the top-level Django project directory based on the current environment. It looks for module containing the currently- active settings module, in both pre-1.4 and post-1.4 layours. """

    projname = settings.SETTINGS_MODULE.split(".",1)[0]
    projmod = import_module(projname)
    projdir = os.path.dirname(projmod.__file__)

    # For Django 1.3 and earlier, the manage.py file was located
    # in the same directory as the settings file.
    if os.path.isfile(os.path.join(projdir,"manage.py")):
        return projdir

    # For Django 1.4 and later, the manage.py file is located in
    # the directory *containing* the settings file.
    projdir = os.path.abspath(os.path.join(projdir, os.path.pardir))
    if os.path.isfile(os.path.join(projdir,"manage.py")):
        return projdir

    msg = "Unable to determine the Django project directory;"\
          " use --project-dir to specify it"
    raise RuntimeError(msg)