如何将这组while循环转换为一个大的while循环，每个测试验证用户名？任何帮助，将不胜感激！
username = input("Please enter a username: ")
while len(username) < 8 or len(username) > 15:
print("Username must be between 8 and 15 characters long.")
username = input("Please enter a username: ")
while username.isalpha() == False:
print ("Username can only contain alphanumeric characters.")
username = input("Please enter a username: ")
while username.islower() == False:
print ("Usernames must contain at least one lowercase character")
username = input("Please enter a username: ")
while username.isupper() == False:
print ("Usernames must contain at least one uppercase character")
username = input("Please enter a username: ")
while username.isnumeric() == False:
print ("Usernames must contain at least one numeric character")
username = input("Please enter a username: ")
firstch = username([0])
lastch = username([-1])
while firstch.isnumeric == True:
print ("The first character in a username cannot be a digit")
username = input("Please enter a username: ")
while lastch.isnumeric == True:
print ("The last character in a username cannot be a digit")
username = input("Please enter a username: ")
break
答案 0 :(得分：3)
除非您完全打算对每一次检查发出警告（我可能只是验证它，然后一次显示规则），您可以使用以下内容：
from unicodedata import category
username = input('Please enter a username: ')
valid = bool(
# Length check
8 <= len(username) <= 15
# No digits for first or last character
and not username[0].isdigit()
and not username[-1].isdigit()
# Consists of only uppercase, lowercase or digits - but at least one of each
and {'Lu', 'Ll', 'Nd'} == {category(ch) for ch in username}
)
答案 1 :(得分：2)
将整个输入过程放入一个while循环中，并使用单个if语句检查条件：
username_is_valid = False
while not username_is_valid:
username = input("Please enter a username: ")
if len(username) < 8 or len(username) > 15:
print("Username must be between 8 and 15 characters long.")
continue
if not username.isalpha():
print ("Username can only contain alphanumeric characters.")
continue
if not username.islower():
print ("Usernames must contain at least one lowercase character")
continue
if not username.isupper():
print ("Usernames must contain at least one uppercase character")
continue
if not username.isnumeric():
print ("Usernames must contain at least one numeric character")
continue
firstch = username([0])
lastch = username([-1])
if firstch.isnumeric:
print ("The first character in a username cannot be a digit")
continue
if lastch.isnumeric:
print ("The last character in a username cannot be a digit")
continue
break
print("Username is valid!")
修改
我看到你的一些条件是错的。例如：
对于相同的输入， username.islower()和username.isupper()永远不会成立。看看@ John的解决方案答案。
正如@zondo所说，你也可以简化你的布尔检查（请将你的条件与我的比较）
答案 2 :(得分：2)
checks = [
(lambda: 8 <= len (username) <= 15, 'Username must be between 8 and 15 characters long.'),
(lambda: username.isalpha (), 'Username can only contain alphanumeric characters.'),
# And so on, you get the idea, it is very simple to expand this list and you can even make it dynamic.
]
while True:
username = input ('Please enter a username: ')
for check in checks:
if not check [0] ():
print (check [1])
break
else:
break
答案 3 :(得分：1)
在我看来，更合理的结构方式是
username_is_valid = False
while not username_is_valid:
username = input("Please enter a username: ")
if len(username) < 8 or len(username) > 15:
print("Username must be between 8 and 15 characters long.")
elif username.isalpha() == False:
print ("Username can only contain alphanumeric characters.")
else:
username_is_valid = True
你的一些逻辑也没有以你想要的方式工作，例如username.isupper()应写成
import string
if not any(c in username for c in string.ascii_uppercase):
print("username needs one uppercase character")
这是一个更完整的解决方案
username_is_valid = False
while not username_is_valid:
username = input("Please enter a username: ")
if len(username) < 8 or len(username) > 15:
print("Username must be between 8 and 15 characters long.")
elif not username.isalnum():
print("Username can only contain alphanumeric characters.")
elif not any(c.islower() for c in username):
print("Usernames must contain at least one lowercase character")
elif not any(c.isupper() for c in username):
print("Usernames must contain at least one uppercase character")
elif not any(c.isdigit() for c in username):
print("Usernames must contain at least one numeric character")
elif username[0].isdigit():
print("The first character in a username cannot be a digit")
elif username[-1].isdigit():
print("The last character in a username cannot be a digit")
else:
username_is_valid = True
答案 4 :(得分：0)
def check_len(name):
return (len(name) >= 8) and (len(name) <= 15)
conds = [check_len, str.isalpha, str.islower, ...] #conditions for the name in general
msgs = ["Username must be between 8 and 15 characters long.", \
"Username can only contain alphanumeric characters.", \
...] #corresponding error messages
parsed = False
while True:
uname = input('Please enter username: ')
for i in range(len(conds)):
func = conds[i]
if not func(uname): # call each function on the username
print(msgs[i]) # print the corresponding err msg
break
else:
parsed = True # initial checks are done
if not parsed: # else restart the loop
continue
if uname[0].isnumeric() or uname[-1].isnumeric():
print('No digits in first or last character!")
parsed = False
continue
答案 5 :(得分：0)
您的验证存在一些问题，例如username.islower()断言整个字符串较低，而不仅仅是字符串中的字符。可以通过扫描any(c.islower() for c in username)等字符串来修复这些问题。然后，每次提示输入用户名时都不检查所有条件，你根本就没有验证它。
这是一个while循环，通过记录输入错误来跟踪故障。它一次性为用户提供所有坏消息，以便解决所有问题。它的可读性更高。
while 1:
username = input("Please enter user name: ")
errs = []
if len(username) < 8 or len(username) > 15:
errs.append("be between 8 and 15 characters long")
if not username.isalnum():
errs.append("only contain alphanumeric characters")
if not any(c.lower() for c in username):
errs.append("contain at least one lowercase character")
if not any(c.upper() for c in username):
errs.append("contain at least one uppercase character")
if not any(c.isnumeric() for c in username):
errs.append("contain at least one numeric character")
if username[0].isnumeric():
errs.append("not have digit as first character")
if username[-1].isnumeric():
errs.append("not have digit as last character")
if errs:
errs.insert(0, "Invalid. Username must...")
print("\n ..".join(errs))
else:
break