限制用户输入中的数字量

Question

I'm making a 4 digit password guesser in python 3. I want to make sure that you can only put in 4 digit passwords and not 5 or 6 digit passwords. Here is the code I have so far.

print('your password will not be used or saved for later use you do   not have to put in your real password')
real_password = int(input("please enter your four digit phone password here:"))
computer_guess = 0000
guess_counter = 0
yes = 'yes'
no = 'no'
print ("guessing your password...")
while computer_guess < real_password:
    computer_guess = computer_guess + 1
    guess_counter = guess_counter + 1
    print("guess number", guess_counter)
print ("your password is", computer_guess)

Answer 1

Before you cast the input to an int, cast it to a str instead, then you can call the len() builtin method to check the length of the entered string. Check the documentation for details on this method. If it is greater than 4, then you should recall your input call. Something like the following should work:

>>> real_password = input("please enter your four digit phone password here: ")
please enter your four digit phone password here: 1234
>>> while len(str(real_password)) != 4:
...     real_password = input("please enter your four digit phone  password here: ")

In this condition the loop would not be ran, however if the entered string was not equal to 4, the loop would run until that condition was satisfied.

Answer 2

print('your password will not be used or saved for later use you do   not have to put in your real password')

def get_password():
    real_password = int(input("please enter your four digit phone password here:"))
    if len(str(real_password)) != 4: # condition is not met if your variable
        get_password()               # is not 4, easily changed if you  
    else:                            # want
        return real_password

#define a method and ask it to call itself until a condition is met 
#

real_password = get_password() # here the method is called and the return
computer_guess = 0             # value is saved as 'real_password'
guess_counter = 0
yes = 'yes'                    # these are not used in your code
no = 'no'                      # but I'm am sure you knew that
print ("guessing your password...")
while computer_guess != real_password: # your loop should break when the 
    computer_guess += 1                # is found, not some other implied
    guess_counter += 1                 # the '+=' operator is handy  
    print("guess number", guess_counter) 
print ("your password is", str(computer_guess)) # explicitly define the int 
                                                # as a string

I hope that helped...