使用简单的 while 循环时遇到问题

Question

I've been trying to create a simple program in python in which the user is asked for their postcode until it contains both letters and numbers. This is the code I have so far:

num = False
letter = False
while num == False and letter == False:
    postcode = input("what is your postcode? ")
    for i in postcode:
        if i.isalpha:
            letter = True
        if i.isdigit:
            num = True

When I run the program it doesn't ask me for my postcode even when it is wrong. How can I fix this?

Answer 1

You have to call the methods!

if i.isalpha():  # note the ()
    # ...
if i.isdigit():
    # ...

i.isalpha is just the method object (which is always truthy). Only calling it will produce the real bool you are looking for.

You could actually make this more concise, all the while not manually calling the methods and not having to maintain/reset all those variables:

while True:
    postcode = input("what is your postcode? ")
    if any(map(str.isalpha, postcode)) and any(map(str.isdigit, postcode)):
        break

Answer 2

Took me a while to see all the problems.

num = False
letter = False
while not(num and letter):
    num = False
    letter = False
    user_input = input("What is your postcode? ")
    x = user_input[0]
    y = user_input[1]
    print(x.isalpha())
    print(y.isdigit())
    if x.isalpha():
        letter = True
    if y.isdigit():
        num = True
    print(num, letter)
        
print("You are in")

You don't reset the values of num and letter each time.

In your original you are changing a string you are iterating over.

And as someone else pointed out, you need to call functions with () .

A good attempt though. There are many ways this could be done. Mine is just one "fix".