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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 is_valid_size(size, chunk_size):
 """Validate max theoretical size."""

        min_csize = current_app.config['FILES_REST_MULTIPART_CHUNKSIZE_MIN']
        max_size = \
            chunk_size * current_app.config['FILES_REST_MULTIPART_MAX_PARTS']
        return size > min_csize and size <= max_size