定义函数：

1 def greet_users(names): #names是形参
2     """Print a simple greeting to each user in the list."""
3     for name in names:
4         msg = "Hello, " + name.title() + "!"
5         print(msg)
6 
7 usernames = ['hannah', 'ty', 'margot']
8 greet_users(usernames)#usernames是实参

关键字def来定义一个函数。实参是调用函数时传递给函数的的信息。

调用函数时，把实参传递给函数，这个值被存储在形参中。PS:大脑中有这个概念，至于如何使用，按实际情况来考虑。

传递实参：

 1 def describe_pet(pet_name, animal_type='dog'):
#关联方式：位置实参；animal_type指定了默认名。若调用函数未给形参提供实参，则使用默认名。
 2     """Display information about a pet."""
 3     print("\nI have a " + animal_type + ".")
 4     print("My " + animal_type + "'s name is " + pet_name.title() + ".")
 5     
 6 # A dog named Willie.
 7 describe_pet('willie')
 8 describe_pet(pet_name='willie')
 9 
10 # A hamster named Harry.
11 describe_pet('harry', 'hamster')
12 describe_pet(pet_name='harry', animal_type='hamster')
#使用关键词实参，务必准确地指定函数定义的形参名
13 describe_pet(animal_type='hamster', pet_name='harry')

• 1.调用函数多次
• 2.位置实参的顺序很重要

 返回值：

 1 def get_formatted_name(first_name, last_name, middle_name=''):、
#让实参变成可选的，形参=‘空字符串’。
 2     """Return a full name, neatly formatted."""
 3     if middle_name:
 4         full_name = first_name + ' ' +  middle_name + ' ' + last_name
 5     else:
 6         full_name = first_name + ' ' + last_name
 7     return full_name.title()  #返回
 8     
 9 musician = get_formatted_name('jimi', 'hendrix')
10 print(musician)
11 
12 musician = get_formatted_name('john', 'hooker', 'lee')
13 print(musician)

 返回字典：

1 def build_person(first_name, last_name, age=''):
2     """Return a dictionary of information about a person."""
3     person = {'first': first_name, 'last': last_name}
4     if age:
5         person['age'] = age
6     return person
7 #返回字典，将值封装到字典中
8 musician = build_person('jimi', 'hendrix', age=27)
9 print(musician)

传递列表：

将列表传递给函数后，函数能直接访问其内容。

1 def greet_users(names):
2     """Print a simple greeting to each user in the list."""
3     for name in names:
4         msg = "Hello, " + name.title() + "!"
5         print(msg)
6 
7 usernames = ['hannah', 'ty', 'margot'] #列表调用定义的函数，将列表传递给形参。
8 greet_users(usernames)

在函数中修改列表：

 1 def print_models(unprinted_designs, completed_models):                 #定义函数1
 2     """
 3     Simulate printing each design, until there are none left.
 4     Move each design to completed_models after printing.
 5     """
 6     while unprinted_designs:
 7         current_design = unprinted_designs.pop()
 8     
 9         # Simulate creating a 3d print from the design.
10         print("Printing model: " + current_design)
11         completed_models.append(current_design)      #在函数中修改列表
12         
13 def show_completed_models(completed_models):                       #定义函数2
14     """Show all the models that were printed."""
15     print("\nThe following models have been printed:")
16     for completed_model in completed_models:
17         print(completed_model)
18         
19         
20 unprinted_designs = ['iphone case', 'robot pendant', 'dodecahedron']
21 completed_models = []
22 
23 print_models(unprinted_designs, completed_models)
24 show_completed_models(completed_models)

 导入函数：

from 模块 import 函数 as 简标记

*代表所有函数