LPTHW ex 40 不工作？ （字典练习，不返回键：值对。）

Question

我对我的代码进行了三次检查，据我所知，它与书中给出的 ex40 基本相同（LPTHW，Python 2.7）：

cities = {'CA': 'San Francisco', 'MI': 'Detroit', 'FL': 'Jacksonville'}

cities['NY'] = 'New York'
cities['OR'] = 'Portland'

def find_city(themap, state):
        if state in themap:
            return themap[state]
    else:
        return "Not found."

cities['_find'] = find_city

while True:
    print "State? (ENTER to quit)",
    state = raw_input("> ")

    if not state: break

city_found = cities['_find'](cities, state)
print city_found

预期的输出是这样的：

State? (ENTER to quit) > CA
San Francisco
State? (ENTER to quit) > FL
Jacksonville
State? (ENTER to quit) > O
Not found.
State? (ENTER to quit) > OR
Portland
State? (ENTER to quit) > VT
Not found.
State? (ENTER to quit) >

但是当我运行它时，输入行只是重复，直到我在空白行上按回车，从不产生城市。像这样：

State? (Enter to quit) > KS
State? (Enter to quit) > NY
State? (Enter to quit) > LA
State? (Enter to quit) > CA
State? (Enter to quit) > 
Not found.

谁能告诉我我忽略了什么？

谢谢。

Answer 1

线条

city_found = cities['_find'](cities, state) # Better: city_found = find_city(cities, state)
print city_found

需要在 while 循环内，而不是在它之后。

我完全不明白cities['_find'] = find_city 的目的是什么——为什么不直接调用该函数而不是将其添加到城市字典中呢？对我来说似乎非常不合时宜。