使用字典創建凱撒密碼，只輸出一項

對于課程，我正在創建一個函式，該函式在給定的移位后將字母表中的每個字母轉換為其相應的字母，這種方式凱撒密碼會移位每個字母。到目前為止，我有：

alphabet = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']


# Problem 1.

def build_cipher(shift):
    '''
    Description: takes in shift (an integer representing the amount the letter key in the dictionary is shifted from its corresponding letter) and returns a dictionary containing all letters and their corresponding letters after the shift. This is acheived through subtracting the shift from the number corresponding to the letter, and using modulo 26.
    
    >>> build_cipher(3)
    
    '''
    
    for i in range(0, 26):
        letter = alphabet[i]
        shiftedletter = alphabet[(i - shift) % 26]
      
        return {letter : shiftedletter}

這大部分是正確的，但它只輸出：

{'a': 'x'}

我怎樣才能讓它為每個字母輸出？我希望我的輸出是：

{‘a’: ‘x’,
‘b’: ‘y’,
‘c’: ‘z’,
‘d’: ‘a’,
‘e’: ‘b’,
‘f’: ‘c’,
‘g’: ‘d’,
‘h’: ‘e’,
‘i’: ‘f’,
‘j’: ‘g’,
‘k’: ‘h’,
‘l’: ‘i’,
‘m’: ‘j’,
‘n’: ‘k’,
‘o’: ‘l’,
‘p’: ‘m’,
‘q’: ‘n’,
‘r’: ‘o’,
‘s’: ‘p’,
‘t’: ‘q’,
‘u’: ‘r’,
‘v’: ‘s’,
‘w’: ‘t’,
‘x’: ‘u’,
‘y’: ‘v’,
‘z’: ‘w’}

我認為問題在于它沒有為字母表中的每個字母回圈，但我不確定如何解決這個問題。任何幫助表示贊賞，謝謝！

uj5u.com熱心網友回復：

您想先構建字典。完成后，回傳剛剛構建的字典。

def build_cipher(shift):
    cipher = dict()
    for i in range(0, 26):
        letter = alphabet[i]
        shiftedletter = alphabet[(i - shift) % 26]
        cipher[letter] = shiftedletter
    return cipher

或者，作為一種理解：

def build_cipher(shift):
    return {alphabet[i]: alphabet[(i - shift) % 26] for i in range(0, 26)}

uj5u.com熱心網友回復：

作為替代方案，您可以使用任何移位值str.maketrans()制作轉換表t：

def make_table(alpha, shift):
    k = shift % len(alpha)
    return str.maketrans(alpha, alpha[k:]   alpha[:k])

然后用于s.translate(t)翻譯任何字串s：

In [1]: s = "hello world"

In [2]: alpha = "abcdefghijklmnopqrstuvwxyz"

In [3]: t = make_table(alpha, 13)

In [4]: s.translate(t)
Out[4]: 'uryyb jbeyq'

In [5]: t = make_table(alpha, -42)

In [8]: s.translate(t)
Out[8]: 'rovvy gybvn'

uj5u.com熱心網友回復：

這是解決問題的一種方法。

alphabet = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

# Problem 1.

def build_cipher(shift):
result = {}
for i in range(0, 26):
    letter = alphabet[i]
    shiftedletter = alphabet[(i - shift) % 26]
  
    result.update({letter : shiftedletter})
return result

uj5u.com熱心網友回復：

一個簡單的解決方案，可以修復您的代碼。

def build_cipher(shift):
    '''
    Description: takes in shift (an integer representing the amount the letter
    key in the dictionary is shifted from its corresponding letter) and returns
    a dictionary containing all letters and their corresponding letters after
    the shift. This is acheived through subtracting the shift from the number
    corresponding to the letter, and using modulo 26.

    >>> build_cipher(3)
    '''

    alphabet = [
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
        'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
    ]

    cipher = {}
    for i in range(0, 26):
        cipher[alphabet[i]] = alphabet[(i - shift) % 26]

    return cipher

cipher = build_cipher(3)
for k,v in cipher.items():
    print("{}: {}".format(k, v))

輸出：

a: x
b: y
c: z
d: a
e: b
f: c
g: d
h: e
i: f
j: g
k: h
l: i
m: j
n: k
o: l
p: m
q: n
r: o
s: p
t: q
u: r
v: s
w: t
x: u
y: v
z: w

uj5u.com熱心網友回復：

你第一次呼叫return它的那一刻就會跳出函式。您可以將 return 陳述句更改為列印陳述句，也可以將回傳字串部分放在回圈中。像這樣的東西：

ret = ""
for i in range(0, 26):
    letter = alphabet[i]
    shiftedletter = alphabet[(i - shift) % 26]
    ret  = "{"   letter    " : "   shiftedletter   "}\n"
return ret

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