篩選一些特殊字符

Question

直到現在，當用戶在我的應用程序中註冊時，他無法創建具有特殊字符的用戶名。我不喜歡這樣寫道：

if username.isalnum() is False: 
.... 

但現在我希望能夠像的特殊字符列表：! - _ $。

什麼是正確的做法？

Answer 1

這段代碼將打印壞字符

username = 'test343!_$&^ffg' 
character_allowed = ['!', '_', '-', '$'] 
for letter in username: 
    if not (letter.isalpha() or letter.isdigit() or letter in character_allowed): 
     print letter 

Answer 2

如果使用了錯誤的字符並將其刪除，此代碼將會發出警報。

a = "username$" 
b = "! - _ $" #can be a string, list or set 

#alert if bad chars 
for c in b: 
    if c in a: 
     print c + " is a bad character" 
     break 

#short alert code 
if any((c in a) for c in b): print c + " is a bad character" 

#remove bad chars 
for c in b: a=a.replace(c,"") 

print a 

Answer 3

一個無效字符不是字母數字and它不是在允許的特殊字符。

name = 'GrandGTO$@' 
valid_chars = set('! - _ $') 

for char in name: 
    if not char.isalnum() and char not in valid_chars: 
     print(char, 'is invalid.') 
     break