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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 clear_file_cache(filename=None):
 """Clear the file cache. If no filename is given clear it entirely. if a filename is given, clear just that filename."""

    global file_cache, file2file_remap, file2file_remap_lines
    if filename is not None:
        if filename in file_cache:
            del file_cache[filename]
            pass
    else:
        file_cache = {}
        file2file_remap = {}
        file2file_remap_lines = {}
        pass
    return