
flake8 results: ``` ./ciphers/playfair_cipher.py:88:25: F821 undefined name 'chunk' for char1, char2 in chunk(ciphertext, 2): ^ ```
flake8 results: ``` ./ciphers/playfair_cipher.py:88:25: F821 undefined name 'chunk' for char1, char2 in chunk(ciphertext, 2): ^ ```