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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 _calc_dir_size(path):
 """ Calculate size of all files in `path`. Args: path (str):
 Path to the directory. Returns: int: Size of the directory in bytes. """

    dir_size = 0
    for (root, dirs, files) in os.walk(path):
        for fn in files:
            full_fn = os.path.join(root, fn)
            dir_size += os.path.getsize(full_fn)

    return dir_size