零散的知识点
0, None, 空字符串"", 空列表[], 空元组(), 空字典{} 的布尔值都是False
函数可以做为变量,参数用(x)写在后面
def find_city:
pass
cities['_find'] = find_city
# 向字典cities插入键值
city_found = cities['_find'](cities, state)
# 从字典cities中提取'_find'的键值即函数find_city，函数参数是(cities, state)
How to become a proficient Python programmer
http://blog.dispatched.ch/2011/06/12/how-to-become-a-proficient-python-programmer/
Welcome to Python for you and me
http://pymbook.readthedocs.org/en/latest/
Real Python
Full Stack Python
http://www.fullstackpython.com/best-python-resources.html