def build_coder(shift): 
 """ 
 Returns a dict that can apply a Caesar cipher to a letter. 
 The cipher is defined by the shift value. Ignores non-letter characters 
 like punctuation and numbers. 
 shift: -27 < int < 27 
 returns: dict 
 Example: >>> build_coder(3) 
 {' ': 'c', 'A': 'D', 'C': 'F', 'B': 'E', 'E': 'H', 'D': 'G', 'G': 'J', 
 'F': 'I', 'I': 'L', 'H': 'K', 'K': 'N', 'J': 'M', 'M': 'P', 'L': 'O', 
 'O': 'R', 'N': 'Q', 'Q': 'T', 'P': 'S', 'S': 'V', 'R': 'U', 'U': 'X', 
 'T': 'W', 'W': 'Z', 'V': 'Y', 'Y': 'A', 'X': ' ', 'Z': 'B', 'a': 'd', 
 'c': 'f', 'b': 'e', 'e': 'h', 'd': 'g', 'g': 'j', 'f': 'i', 'i': 'l', 
 'h': 'k', 'k': 'n', 'j': 'm', 'm': 'p', 'l': 'o', 'o': 'r', 'n': 'q', 
 'q': 't', 'p': 's', 's': 'v', 'r': 'u', 'u': 'x', 't': 'w', 'w': 'z', 
 'v': 'y', 'y': 'a', 'x': ' ', 'z': 'b'} 
 (The order of the key-value pairs may be different.) 
 """ 
 ### YOUR CODE GOES HERE

  
def build_encoder(shift): 
 """ 
 Returns a dict that can be used to encode a plain text. For example, you 
 could encrypt the plain text by calling the following commands 
 >>>encoder = build_encoder(shift) 
 >>>encrypted_text = apply_coder(plain_text, encoder) 
 The cipher is defined by the shift value. Ignores non-letter characters 
 like punctuation and numbers. 
 shift: 0 <= int < 27 
 returns: dict 
 Example: >>> build_encoder(3) 
 {' ': 'c', 'A': 'D', 'C': 'F', 'B': 'E', 'E': 'H', 'D': 'G', 'G': 'J', 
 'F': 'I', 'I': 'L', 'H': 'K', 'K': 'N', 'J': 'M', 'M': 'P', 'L': 'O', 
 'O': 'R', 'N': 'Q', 'Q': 'T', 'P': 'S', 'S': 'V', 'R': 'U', 'U': 'X', 
 'T': 'W', 'W': 'Z', 'V': 'Y', 'Y': 'A', 'X': ' ', 'Z': 'B', 'a': 'd', 
 'c': 'f', 'b': 'e', 'e': 'h', 'd': 'g', 'g': 'j', 'f': 'i', 'i': 'l', 
 'h': 'k', 'k': 'n', 'j': 'm', 'm': 'p', 'l': 'o', 'o': 'r', 'n': 'q', 
 'q': 't', 'p': 's', 's': 'v', 'r': 'u', 'u': 'x', 't': 'w', 'w': 'z', 
 'v': 'y', 'y': 'a', 'x': ' ', 'z': 'b'} 
 (The order of the key-value pairs may be different.) 
 HINT : Use build_coder. 
 """ 
 ### YOUR CODE GOES HERE

  
def build_decoder(shift): 
 """ 
 Returns a dict that can be used to decode an encrypted text. For example, 
you 
 could decrypt an encrypted text by calling the following commands 
 >>>encoder = build_encoder(shift) 
 >>>encrypted_text = apply_coder(plain_text, encoder) 
 >>>decrypted_text = apply_coder(plain_text, decoder) 
 The cipher is defined by the shift value. Ignores non-letter characters 
 like punctuation and numbers. 
 shift: 0 <= int < 27 
 returns: dict 
 Example: >>> build_decoder(3) 
 {' ': 'x', 'A': 'Y', 'C': ' ', 'B': 'Z', 'E': 'B', 'D': 'A', 'G': 'D', 
 'F': 'C', 'I': 'F', 'H': 'E', 'K': 'H', 'J': 'G', 'M': 'J', 'L': 'I', 
 'O': 'L', 'N': 'K', 'Q': 'N', 'P': 'M', 'S': 'P', 'R': 'O', 'U': 'R', 
 'T': 'Q', 'W': 'T', 'V': 'S', 'Y': 'V', 'X': 'U', 'Z': 'W', 'a': 'y', 
 'c': ' ', 'b': 'z', 'e': 'b', 'd': 'a', 'g': 'd', 'f': 'c', 'i': 'f', 
 'h': 'e', 'k': 'h', 'j': 'g', 'm': 'j', 'l': 'i', 'o': 'l', 'n': 'k', 
 'q': 'n', 'p': 'm', 's': 'p', 'r': 'o', 'u': 'r', 't': 'q', 'w': 't', 
 'v': 's', 'y': 'v', 'x': 'u', 'z': 'w'} 
 (The order of the key-value pairs may be different.) 
 HINT : Use build_coder. 
 """ 
 ### YOUR CODE GOES HERE

  
def apply_coder(text, coder): 
 """ 
 Applies the coder to the text. Returns the encoded text. 
 text: string 
 coder: dict with mappings of characters to shifted characters 
 returns: text after mapping coder chars to original text 
 Example: 
 >>> apply_coder("Hello, world!", build_encoder(3)) 
 'Khoor,czruog!' 
 >>> apply_coder("Khoor,czruog!", build_decoder(3)) 
 'Hello, world!' 
 """ 
  ### YOUR CODE GOES HERE

  
def apply_shift(text, shift): 
 """ 
 Given a text, returns a new text Caesar shifted by the given shift 
 offset. The empty space counts as the 27th letter of the alphabet, 
 so spaces should be replaced by a lowercase letter as appropriate. 
 Otherwise, lower case letters should remain lower case, upper case 
 letters should remain upper case, and all other punctuation should 
 stay as it is. 
 text: string to apply the shift to 
 shift: amount to shift the text 
 returns: text after being shifted by specified amount. 
 Example: 
 >>> apply_shift('This is a test.', 8) 
 'Apq hq hiham a.' 
 """ 
 ### YOUR CODE GOES HERE