Python的random.choice方法如何避免重复？

Question

我正在尝试改进这段代码，它会在给出一个州的时候要求用户说出该州的首府，但我注意到有时它会重复一个州并询问两次。

我尝试使用random.sample代替，但是我得到了一个错误"TypeError: Unhashable type: 'list'"。下面是可以工作但会重复的代码，其中random.sample被注释掉了：

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.')

我也尝试过只使用字典名称capitals_dict，像这样：

random.sample(capitals_dict, 5)

但是我遇到了一个不同的错误，然后发现我不能像那样使用字典。

- cisconethead

---

你得到的错误是因为你正在使用列表作为索引，capital = capitals_dict[state]。你可以在进入循环之前使用random.shuffle(states)来对列表进行原地洗牌。然后，只需按顺序从中选择状态即可。 - Spice

抱歉，我不小心使用了Python 2.. 不过错误信息确实告诉你可以做什么。 - Martijn Pieters

Answer 1

您可以通过首先将字典传递给 list() 函数，然后从该列表中进行抽样来创建字典中所有键的列表：

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

您还可以传入 dict.keys() 字典视图:

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

但在内部，random.sample() 也会将其转换为一个序列（一个 tuple()），因此在这里使用 list() 实际上更有效率。

你遇到的异常实际上是在告诉你这个信息：

>>> 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).
#                                                 ^^^^^^^^^^^^^^^^^^^^^^^

演示:

>>> 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']

要将其纳入您的代码中：

导入随机模块。

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))

我还将您的字符串连接替换为str.format()调用，以便将值放入字符串模板中。

- Martijn Pieters

---

这是我基于你的代码尝试的内容：states = list(capitals_dict) for i in [1, 2, 3, 4, 5]: 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 + '.') - cisconethead

@cisconethead：但是state在那里是一个列表。所以下一行执行的是capitals_dict[['Maryland', 'Mississippi', 'Wisconsin', 'Texas', 'West Virginia']]，这将失败，因为您不能使用列表作为键。 - Martijn Pieters

Answer 2

尝试以这种方式进行。它只是对州名进行抽样：

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.')

虽然你也可以使用：

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

因为list(dictionary)会隐式地返回一个字典键的列表，但我更喜欢使过程显式。

- martineau

---

@Martijn：说得好，但我认为在我的修改中使用capitals_dict.keys()更加明确。 - martineau

@Martijn：我从random.sample()没有收到错误信息。 - martineau

@Martijn：这就是我正在使用的版本，3.4.2。 - martineau

没错，但是 random.sample() 函数抛出类型错误时给了你特定的建议：TypeError: Population must be a sequence or set. For dicts, use list(d). 参见源代码；在此处，字典视图是 Set ABC 的一个实例。 - Martijn Pieters

@martineau，这看起来也很不错。我会尝试两种方法来了解它们的区别。虽然我对编程非常陌生，但我喜欢有这么多编码方式！ - cisconethead

Answer 3

如果有人想要一个不错的美国州府测验程序，我已经更新了代码，包括跟踪用户得分。它会随机询问所有50个州，而且你也可以随时跳过或退出。

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)')

- cisconethead