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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 gethash(compiled):
 """Retrieve a hash from a header."""

    lines = compiled.splitlines()
    if len(lines) < 3 or not lines[2].startswith(hash_prefix):
        return None
    else:
        return lines[2][len(hash_prefix):]