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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 backup(path, password_file=None):
 """ Replaces the contents of a file with its decrypted counterpart, storing the original encrypted version and a hash of the file contents for later retrieval. """

    vault = VaultLib(get_vault_password(password_file))
    with open(path, 'r') as f:
        encrypted_data = f.read()

        # Normally we'd just try and catch the exception, but the
        # exception raised here is not very specific (just
        # `AnsibleError`), so this feels safer to avoid suppressing
        # other things that might go wrong.
        if vault.is_encrypted(encrypted_data):
            decrypted_data = vault.decrypt(encrypted_data)

            # Create atk vault files
            atk_path = os.path.join(ATK_VAULT, path)
            mkdir_p(atk_path)
            # ... encrypted
            with open(os.path.join(atk_path, 'encrypted'), 'wb') as f:
                f.write(encrypted_data)
            # ... hash
            with open(os.path.join(atk_path, 'hash'), 'wb') as f:
                f.write(hashlib.sha1(decrypted_data).hexdigest())

            # Replace encrypted file with decrypted one
            with open(path, 'wb') as f:
                f.write(decrypted_data)