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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 get_password_hash(username):
 """ Fetch a user's password hash. """

    try:
        h = spwd.getspnam(username)
    except KeyError:
        return None

    # mitogen.core.Secret() is a Unicode subclass with a repr() that hides the
    # secret data. This keeps secret stuff out of logs. Like blobs, secrets can
    # also be serialized.
    return mitogen.core.Secret(h)