简单的Python游戏无论如何都无法正常工作

Question

I been trying to write a Python program that implements the cows bulls game, here's my code:

import random
def cb():
  pc = random.sample('123456789',4)
  cows = []
  bulls = []
  while True:
    guess = input('please enter a 4 digit num: ')
    cows = rmd(cows)
    bulls = rmd(bulls)
    if pc == guess:
      print('You win!')
      break
    (cows.append(i) for i in pc if i in guess and guess.index(i) == pc.index(i))
    (bulls.append(i) for i in pc if i in guess and guess.index(i) != pc.index(i))
    print ('{} cows and {} bulls'.format(len(cows), len(bulls))
    continue

Just the last approach I tried before giving up, before that I wrote more than 50 programs and nothing would work, it would always return 0 cows 0 bulls. I have tried for loops while guess!=pc among hundreds of ideas.. Nothing would work.

rmd is a function that removes duplicate items from a given list by converting it to a set and then converting that set to a list and returns the final list.

It's just a silly game but the fact that nothing works is very depressing..

Answer 1

random.sample returns a list, so it will never be equal to the string the user enters.

The lines (cows.append(i)... and (bulls.append(i)... are generators, meaning that they do nothing unless and until they are evaluated. You could technically turn them into list comprehensions by swapping the enclosing parentheses for square brackets, but you would be building up a list for its side effects, which is frowned upon. Instead of putting a list.append in a generator or comprehension, make a comprehension that actually builds the list you want, as they're intended to do. Additionally, since you only want the unique items in the first place, there's no reason to use lists at any point.

There's also no reason to build lists or sets at all, since all you want to do is count up each instance.

import random

def cb():
    pc = ''.join(random.sample('123456789',4))
    while True:
        guess = input('please enter a 4 digit num: ')
        if pc==guess:
            print ('You win!')
            break
        bulls = 0
        cows = 0
        for character in guess:
            if character in pc:
                if guess.index(character) == pc.index(character):
                    bulls += 1
                else:
                    cows += 1
        print(cows, 'cows and', bulls, 'bulls')

Answer 2

1. Don't lose heart, starting to program isn't always easy!
2. Use print often to see what's in your variables, you'd be surprised!
3. random.sample('123456789',4) returns a list of 4 letters, not a 4 letter word.
4. input , as opposed to raw_input, attempts automatic conversions (for example entering "1234" would result in an int) and some consider it bad practice. Use raw_input to ensure you get a string.
5. But if you get an int from your input, and a list of strings (or even a string if you joined it properly, using "".join(random.sample....) how can they be equal?!
6. Finally the (... for _ in _) syntax is a generator syntax. Please google it, it's important to understand - it's one of the core constructs in Python. That code will never be evaluated as you use it. People new to Python often try to force the cool syntax wherever they can, even if it makes no sense. This is much nice (IMO):

Code:

for index,i in enumerate(guess):
     if i in guess:
         if pc[index] == i: cows.append(i)
         else:              bulls.append(i)

Good luck! EDIT:

I saw someone solved it for you - I still urge you to read about generators, and maybe a walkthrough.