Question

我正在学习Python并且对if not在下面的代码中做了什么感到困惑？我认为if not就像else一样。但事实证明我错了。此代码中if not exists的值是多少？还有一个天真的问题，变量exists是在for循环中定义的，为什么它在全局范围内可用？

import scrabble
import string

for letter in string.ascii_lowercase:
    for word in scrabble.wordlist:
        exists = False
        if letter * 2 in word:
            exists = True
            break
    if not exists:
        print(letter)

print(exists) # Globally exists = True

Answer 1

以下是一些解释：

import string

# let's create our own wordlist
wordlist = ["cat","moose"]

# Loop all letters from a-z
for letter in string.ascii_lowercase:
    # Inner-loop all words in wordlist
    for word in wordlist:
        # Start with exists = False
        exists = False
        # If letter is repeated break the inner loop and set exists = True
        if letter * 2 in word:
            exists = True
            break
    # Check if exists is False (which it is if double letter didn't exist in any word)
    if not exists:
        print(letter)

# This will print the last exists value (True if 'z' is doubled in any word else false)
print(exists)

由于在wordlist中的任何一个单词中重复的唯一字母是＆＃39; o＆＃39;所有字母除了＆＃39; o＆＃39;打印出来后跟一个假的

a
b
c
d
...
False

顺便说一句，您可以使用此代码段获得相同的结果：

import string

doubleletters = []
wordlist = ["cat","moose"]

# Loop through wordlist and extend the doubleletters list
for word in wordlist:
    doubleletters.extend(i[0] for i in zip(word,word[1:]) if len(set(i)) == 1)

print('\n'.join(i for i in string.ascii_lowercase if i not in doubleletters))

Answer 2

在python中不会翻转布尔值（true或false）的值。 if not x可以读为＆＃34;如果x为false＆＃34;，那么如果exists等于False，if块中的语句将会执行，即如果没有已找到重复的字母。

什么是“如果没有＆＃39;在代码中？

2 个答案: