无效的语法原因由+ = in ternany

Question

使用普通的if else时工作正常

vocab = {"a": "4", "i": "1", "u": "5", "e": "3", "o": "0"}

firstchar_name = input("Your name : ") # give fruit suggestion
fruitfrom_name = input("First Character of your name is {}, write any fruit that started with {} : ".format(firstchar_name[0], firstchar_name[0]))
favorite_number = input("Your favorite one-digit number : ")
date_of_born = input("Input your born date (date-month-year) : ")

to_alay = ""

word = list(fruitfrom_name.lower())
for char in word:
    to_alay += char if char not in vocab else to_alay += vocab[char]

print(to_alay)

错误:

$ python3 telemakita_password.py        
  File "telemakita_password.py", line 12                                                  
    to_alay += char if char not in vocab else to_alay += vocab[char]                      
                                                       ^                                  
SyntaxError: invalid syntax

我想知道为什么+=在工作但不在+=其他地方

Answer 1

因为这不是 if-then-else语句.它是三元运算符表达式(或条件表达式),这是一个表达式.这是表达部分:

char if char not in vocab else vocab[char]

var += ...是不是一种表达,它是语句.这不是问题,我们可以写:

to_alay += char if char not in vocab else vocab[char]

Python将此解释为:

to_alay += (char if char not in vocab else vocab[char])

所以这基本上做你想要的.

运用 dict.get(..)

话虽如此,我认为通过使用.get(..),你可以让生活更轻松:

for char in word:
    to_alay += vocab.get(char, char)

这更像是"自我解释",每次迭代都是为了获得char与vocabdict 中对应的值,如果找不到该键,则回退到char.

我们甚至可以''.join(..)在这里使用:

to_alay = ''.join(vocab.get(char, char) for char in word)