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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 expanduser(path):
 """Expand ~ and ~user constructs. If user or $HOME is unknown, do nothing."""

    if path[:1] != '~':
        return path
    i, n = 1, len(path)
    while i < n and path[i] not in '/\\':
        i = i + 1

    if 'HOME' in os.environ:
        userhome = os.environ['HOME']
    elif 'USERPROFILE' in os.environ:
        userhome = os.environ['USERPROFILE']
    elif not 'HOMEPATH' in os.environ:
        return path
    else:
        try:
            drive = os.environ['HOMEDRIVE']
        except KeyError:
            drive = ''
        userhome = join(drive, os.environ['HOMEPATH'])

    if i != 1:  # ~user
        userhome = join(dirname(userhome), path[1:i])

    return userhome + path[i:]