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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 has_changed (filename):
 """Check if filename has changed since the last check. If this is the first check, assume the file is changed."""

    key = os.path.abspath(filename)
    mtime = get_mtime(key)
    if key not in _mtime_cache:
        _mtime_cache[key] = mtime
        return True
    return mtime > _mtime_cache[key]