The document provides instructions for implementing a Caesar cipher class in Python. It describes initializing the class with a key, and implementing encrypt, decrypt, encrypt_file, and decrypt_file methods. The encrypt and decrypt methods encrypt and decrypt a plaintext/ciphertext string. The encrypt_file and decrypt_file methods take a file, encrypt/decrypt its contents using the cipher, and write it to a new file. Sample code is given to test the class.

1. Directions:
# Caesar Cipher Implementation
Your task in this homework is to construct a class to implement Caesar Cipher
## Specification
### __init__() method
Define attributes that may be used in the following methods, such as key.
### Encrypt Message
The objective of the `encrypt()` method is to encrypt a message using Caesar Cipher. The
method should return the encrypted message.
Started function:
```python
def encrypt(self, plaintext):
'''
Task 1: encrypt plaintext using caesar cipher
'''
return True
```
### Decript Message
The objective of the `decrypt()` method is to decrypt a encrypted message using Caesar Cipher.
The method should return the decrypted message.
Started function:

2. ```python
def decrypt(self, ciphertext):
'''
Task 2: decrypt ciphertext using caesar cipher
'''
return True
```
### Encrypt a File
The objective of the `encrypt_file()` method is to encrypt the content in a file using Caesar
Cipher and then write the encrypted content in another file.
Started function:
```python
def encrypt_file(self, input_filename, output_filename):
'''
Task 3: encrypt the content in a file (input_filename) using caesar cipher
and store the ciphertext in another file (output_filename)
'''
pass
```
### Decrypt a file

3. The objective of the `decrypt_file()` method is to decrypt the content in a file using Caesar
Cipher and then write the decrypted content in another file.
Starter function:
```python
def decrypt_file(self, input_filename, output_filename):
'''
Task 4: decrypt the content in a file (input_filename) using caesar cipher
and store the decrypted text in another file (output_filename)
'''
pass
```
Task:
caesar_cipher.py file
from pathlib import Path
class CaesarCipher:
def __init__(self, key=3):
pass
def encrypt(self, plaintext):
'''
Task 1: encrypt plaintext using caesar cipher
'''

4. return True
def decrypt(self, ciphertext):
'''
Task 2: decrypt ciphertext using caesar cipher
'''
return True
def encrypt_file(self, input_filename, output_filename):
'''
Task 3: encrypt the content in a file (input_filename) using caesar cipher
and store the ciphertext in another file (output_filename)
'''
pass
def decrypt_file(self, input_filename, output_filename):
'''
Task 4: decrypt the content in a file (input_filename) using caesar cipher
and store the decrypted text in another file (output_filename)
'''
pass

5. if __name__ == "__main__":
caesar_cipher = CaesarCipher()
print(caesar_cipher.encrypt('This is a secret message! My password is XYZ.'))
print(caesar_cipher.decrypt('Hello ABC!'))
caesar_cipher.encrypt_file('secret_message.txt', 'encrypted_secret_message.txt')
caesar_cipher.decrypt_file('encrypted_secret_message.txt', 'decrypted_text.txt')
decrypted_text.txt file
Hello, this is a secret message!
Your password is NDSCsx&s091TSxsa^
encrypted_secret_message.txt
Khoor, wklv lv d vhfuhw phvvdjh!
Brxu sdvvzrug lv QGVFva&v091WVavd^
test_caesar_cipher.py
import pytest
from pathlib import Path
from caesar_cipher import CaesarCipher
def test_caesar_cipher_1():
cipher = CaesarCipher()
assert cipher.encrypt('Hi, my name is Weiping.') == 'KL, PB QDPH LV ZHLSLQJ.'
assert cipher.decrypt('WKLV LV D VHFUHW PHVVDJH! PB SDVVZRUG LV ABC.') ==
'THIS IS A SECRET MESSAGE! MY PASSWORD IS XYZ.'
def test_caesar_cipher_2():
cipher = CaesarCipher()
cipher.encrypt_file('secret_message.txt', 'encrypted_secret_message.txt')
path = Path('encrypted_secret_message.txt')
assert path.read_text() == 'KHOOR, WKLV LV D VHFUHW PHVVDJH!nBRXU
SDVVZRUG LV QGVFVA&V091WVAVD^n'
cipher.decrypt_file('encrypted_secret_message.txt', 'decrypted_secret_message.txt')
path = Path('decrypted_secret_message.txt')

6. assert path.read_text() == 'HELLO, THIS IS A SECRET MESSAGE!nYOUR PASSWORD
IS NDSCSX&S091TSXSA^n'