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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 sha1sum_file(filename):
    '''
    Return the secure hash digest with sha1 algorithm for a given file

    >>> from timeside.core.tools.test_samples import samples
    >>> wav_file = samples["C4_scale.wav"]
    >>> print sha1sum_file(wav_file)
    a598e78d0b5c90da54a77e34c083abdcd38d42ba
    '''
    import hashlib
    import io

    sha1 = hashlib.sha1()
    chunk_size = sha1.block_size * io.DEFAULT_BUFFER_SIZE

    with open(filename, 'rb') as f:
        for chunk in iter(lambda: f.read(chunk_size), b''):
            sha1.update(chunk)
    return sha1.hexdigest()