Python random.choice method without repeats?

Question

I'm trying to improve this code which asks the user to say what the state capital is when given a state, but I've noticed that sometimes it will repeat a state and ask it twice.

I tried using random.sample instead, but I got an error "TypeError: Unhashable type: 'list'. Here is the code that works (but repeats) with the random.sample commented out:

capitals_dict = {
    'Alabama': 'Montgomery',
    'Alaska': 'Juneau',
    'Arizona': 'Phoenix',
    'Arkansas': 'Little Rock',
    'California': 'Sacramento',
    'Colorado': 'Denver',
    'Connecticut': 'Hartford',
    'Delaware': 'Dover',
    'Florida': 'Tallahassee',
    'Georgia': 'Atlanta',
    'Hawaii': 'Honolulu',
    'Idaho': 'Boise',
    'Illinois': 'Springfield',
    'Indiana': 'Indianapolis',
    'Iowa': 'Des Moines',
    'Kansas': 'Topeka',
    'Kentucky': 'Frankfort',
    'Louisiana': 'Baton Rouge',
    'Maine': 'Augusta',
    'Maryland': 'Annapolis',
    'Massachusetts': 'Boston',
    'Michigan': 'Lansing',
    'Minnesota': 'St. Paul',
    'Mississippi': 'Jackson',
    'Missouri': 'Jefferson City',
    'Montana': 'Helena',
    'Nebraska': 'Lincoln',
    'Nevada': 'Carson City',
    'New Hampshire': 'Concord',
    'New Jersey': 'Trenton',
    'New Mexico': 'Santa Fe',
    'New York': 'Albany',
    'North Carolina': 'Raleigh',
    'North Dakota': 'Bismarck',
    'Ohio': 'Columbus',
    'Oklahoma': 'Oklahoma City',
    'Oregon': 'Salem',
    'Pennsylvania': 'Harrisburg',
    'Rhode Island': 'Providence',
    'South Carolina': 'Columbia',
    'South Dakota': 'Pierre',
    'Tennessee': 'Nashville',
    'Texas': 'Austin',
    'Utah': 'Salt Lake City',
    'Vermont': 'Montpelier',
    'Virginia': 'Richmond',
    'Washington': 'Olympia',
    'West Virginia': 'Charleston',
    'Wisconsin': 'Madison',
    'Wyoming': 'Cheyenne',
}

import random

states = list(capitals_dict.keys())
for i in [1, 2, 3, 4, 5]:
    state = random.choice(states)
    #state = random.sample(states, 5) 
    capital = capitals_dict[state]
    capital_guess = input('What is the capital of ' + state + '?')

    if capital_guess == capital:
        print('Correct! Nice job!')
    else:
        print('Incorrect.  The Capital of ' + state + ' is ' + capital + '.')

print('All done.')

I also tried just using the dictionary name capitals_dict like this:

random.sample(capitals_dict, 5)

but I got a different error then found out that I can't use dictionaries like that.

Answer 1

If anyone reading this wants a decent US States Capitals quizzer, I updated the code to include tracking the users score. It will ask all 50 states in a random order, and it will also let you skip and quit any time.

capitals_dict = {
    'Alabama': 'Montgomery',
    'Alaska': 'Juneau',
    'Arizona': 'Phoenix',
    'Arkansas': 'Little Rock',
    'California': 'Sacramento',
    'Colorado': 'Denver',
    'Connecticut': 'Hartford',
    'Delaware': 'Dover',
    'Florida': 'Tallahassee',
    'Georgia': 'Atlanta',
    'Hawaii': 'Honolulu',
    'Idaho': 'Boise',
    'Illinois': 'Springfield',
    'Indiana': 'Indianapolis',
    'Iowa': 'Des Moines',
    'Kansas': 'Topeka',
    'Kentucky': 'Frankfort',
    'Louisiana': 'Baton Rouge',
    'Maine': 'Augusta',
    'Maryland': 'Annapolis',
    'Massachusetts': 'Boston',
    'Michigan': 'Lansing',
    'Minnesota': 'St. Paul',
    'Mississippi': 'Jackson',
    'Missouri': 'Jefferson City',
    'Montana': 'Helena',
    'Nebraska': 'Lincoln',
    'Nevada': 'Carson City',
    'New Hampshire': 'Concord',
    'New Jersey': 'Trenton',
    'New Mexico': 'Santa Fe',
    'New York': 'Albany',
    'North Carolina': 'Raleigh',
    'North Dakota': 'Bismarck',
    'Ohio': 'Columbus',
    'Oklahoma': 'Oklahoma City',
    'Oregon': 'Salem',
    'Pennsylvania': 'Harrisburg',
    'Rhode Island': 'Providence',
    'South Carolina': 'Columbia',
    'South Dakota': 'Pierre',
    'Tennessee': 'Nashville',
    'Texas': 'Austin',
    'Utah': 'Salt Lake City',
    'Vermont': 'Montpelier',
    'Virginia': 'Richmond',
    'Washington': 'Olympia',
    'West Virginia': 'Charleston',
    'Wisconsin': 'Madison',
    'Wyoming': 'Cheyenne',
}

import random
counterQuestions = 0 # Represents the number of questions asked to the user
counterCorrect = 0
print('Enter the name of the State Capital with proper spelling.  Enter "skip" to skip or "quit" to quit')
for state in random.sample(list(capitals_dict), 50):
    capital = capitals_dict[state]
    capital_guess = input('What is the capital of {}? '.format(state))
    if capital_guess == 'skip':
        #print('The Capital of {} is {}.'.format(state, capital)) #study mode - use comment feature to turn this on/off.
        counterQuestions = counterQuestions + 1    
        continue
    elif capital_guess == 'quit':
        break
    elif capital_guess == capital:
        print('Correct! Nice job!')
        counterCorrect = counterCorrect + 1
        counterQuestions = counterQuestions + 1
    else:
        print('Incorrect.  The Capital of {} is {}.'.format(state, capital))
        counterQuestions = counterQuestions + 1

score = (counterCorrect / counterQuestions) * 100
counterIncorrect = counterQuestions - counterCorrect
print('All done. Your score is ' + str(score) + '% correct, or ' + str(counterCorrect) + ' out of ' + str(counterQuestions) + ' (' + str(counterIncorrect) + ' incorrect)')

Answer 2

Try doing it this way. which just samples the state names:

import random

num_queries = 5

for state in random.sample(capitals_dict.keys(), num_queries):
    capital = capitals_dict[state]

    capital_guess = input('What is the capital of ' + state + '?')

    if capital_guess == capital:
        print('Correct! Nice job!')
    else:
        print('Incorrect.  The Capital of ' + state + ' is ' + capital + '.')

print('All done.')

While you could also use:

for state in random.sample(list(capitals_dict), num_queries):

because list(dictionary) will implicitly return a list of the dictionary's keys, but I prefer making what's going on explicit.

Answer 3

You can create a list of all keys in the dictionary by passing the dictionary to the list() function first, then sample from that list:

sample = random.sample(list(capitals_dict), 5)

You can also pass in the dict.keys() dictionary view:

sample = random.sample(capitals_dict.keys(), 5)

but internally random.sample() will just convert that to a sequence too (a tuple()) so using list() is actually more efficient here.

The exception you encountered actually tells you this:

>>> random.sample(capitals_dict, 5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/.../lib/python3.4/random.py", line 311, in sample
    raise TypeError("Population must be a sequence or set.  For dicts, use list(d).")
TypeError: Population must be a sequence or set.  For dicts, use list(d).
#                                                 ^^^^^^^^^^^^^^^^^^^^^^^

Demo:

>>> import random
>>> capitals_dict = {
...     'Alabama': 'Montgomery',
...     'Alaska': 'Juneau',
...     'Arizona': 'Phoenix',
...     'Arkansas': 'Little Rock',
...     'California': 'Sacramento',
...     # ... elided ...
... }
>>> 
>>> random.sample(list(capitals_dict), 5)
['Maryland', 'Mississippi', 'Wisconsin', 'Texas', 'West Virginia']

To incorporate that into your code:

import random

for state in random.sample(list(capitals_dict), 5):
    capital = capitals_dict[state]
    capital_guess = input('What is the capital of {}?'.format(state))

    if capital_guess == capital:
        print('Correct! Nice job!')
    else:
        print('Incorrect. The Capital of {} is {}.'.format(state, capital))

I also replaced your string concatenations with str.format() calls to put values into string templates instead.