我的意思是什么？

Question

def CodelandUsernameValidation(s):
  if len(s)>4 and len(s)<25 and s[0].isalpha() and [i for i in s if i.isalnum() or i=="_"]!=[] and s[-1]!="_":
    return True
  else:
    return False
# keep this function call here 
print(CodelandUsernameValidation(input()))

Answer 1

它在s中生成字母数字或下划线字符的列表。该代码实际上是不正确的，因为如果任何字符是字母数字或下划线，它将通过，而其目的肯定是所有字符都必须是字母数字或下划线。这里有一个更好的写作方法：

def CodelandUsernameValidation(s):
  return 4 < len(s) < 25 and s[0].isalpha() and all(i.isalnum() or i=='_' for i in s) and s[-1] != '_'

print(CodelandUsernameValidation(input()))

Answer 2

它是一个list comprehension如果您展开，它将如下所示->

result = []
for i in s: # will fetch element one by one from iterable
    if i.isalnum() or i=="_": # checking condition
        result.append(i) # if true, then append it to the list

上述代码可重写为-

result = [i for i in s if i.isalnum() or i=="_"]