python - 艰难地学习 python 练习 40 帮助

Question

嘿，伙计们，我无法理解这一点，本地图真正引用城市字典时，我不明白。或者最后一行，(cities, state) 部分是什么？

谢谢。

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'

#ok pay attention!
cities['_find'] = find_city

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

    if not state: break

    #this line is the most important ever! study!
    city_found = cities['_find'] (cities, state)
    print city_found

Answer 1

cities['_find'] 就是 find_city。所以 cities['_find'](cities, state) 与 find_city(cities, state) 相同。

我第一个陈述的原因是这一行:

cities['_find'] = find_city

这不会调用 find_city，它会将函数本身粘贴在字典中。 Python 函数只是列表和类实例之类的对象。如果你不在它们后面加上括号，它们可以被赋值给变量。