Python编程：从入门到实践—函数

从函数中修改列表

一家为用户提交的设计制作3D打印模型的公司，需要打印的设计存储在一个列表中，打印后移到另一个列表中。

#!/usr/bin/env python
# -*- coding:utf-8 -*-

unprinted_designs = ['iphone case','robot pendant','dodecahedron']

completed_models = []
while unprinted_designs:
    current_design = unprinted_designs.pop()

    print("Printing model:" + current_design)
    completed_models.append(current_design)

print("\nThe following models have been printed:")
for completed_model in completed_models:
    print(completed_model)

未使用函数的实现方式

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--
def print_models(unprinted_designs,completed_models):
    while unprinted_designs:
        current_design = unprinted_designs.pop()
        completed_models.append(current_design)

def show_completed_models(completed_models):
    print("\nThe following models have been printed:")
    for completed_model in completed_models:
        print(completed_model)

unprinted_designs = ['iphone case','robot pendant','dodecahedron']
completed_models = []

print_models(unprinted_designs,completed_models)
show_completed_models(completed_models)

利用函数实现

采用描述性的函数名；在一个函数中，总是可以调用另一个函数

禁止函数修改列表

切片表示法[:]创建列表的副本，如果不想清空未打印的设计列表，可以这样调用print_models();

print_models(unprinted_designs[:], completed_models)

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--
def print_models(unprinted_designs,completed_models):
    while unprinted_designs:
        current_design = unprinted_designs.pop()
        completed_models.append(current_design)

def show_completed_models(completed_models):
    print("\nThe following models have been printed:")
    for completed_model in completed_models:
        print(completed_model)

unprinted_designs = ['iphone case','robot pendant','dodecahedron']
completed_models = []

print_models(unprinted_designs[0:2],completed_models)
show_completed_models(completed_models)

切片表示法

传递任意数量的实参

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--

def make_pizza(*toppings):
    print(toppings)

make_pizza('peppersoni')
make_pizza('mushrooms','green peppers','extra cheese')

('peppersoni',)
('mushrooms', 'green peppers', 'extra cheese')

运行结果

形参名 *toppings中的星号，让Python创建一个名为toppings的空元组，并将收到的所有值都封装在元组中。

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--

def make_pizza(*toppings):
    print("\nMaking a pizza with the following toppings:")
    for topping in toppings:
        print("- " + topping)

make_pizza('peppersoni')
make_pizza('mushrooms','green peppers','extra cheese')

Making a pizza with the following toppings:
- peppersoni

Making a pizza with the following toppings:
- mushrooms
- green peppers
- extra cheese

运行结果

结合使用位置实参和任意数量实参

　　如果要让函数接收不同类型的实参，必须在函数定义中将接纳任意数量实参的形参放在最后。Python先匹配位置实参和关键字实参，再将余下的实参都收集到最后一个形参中。

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--

def make_pizza(size,*toppings):
    print("\nMaking a " + str(size) + "-inch pizza with the following toppings:")
    for topping in toppings:
        print("- " + topping)

make_pizza(16,'pepppersoni')
make_pizza(12,'mushrooms','green peppers','extra cheese')

Making a 16-inch pizza with the following toppings:
- pepppersoni

Making a 12-inch pizza with the following toppings:
- mushrooms
- green peppers
- extra cheese

位置实参和任意数量实参

使用任意数量的关键字实参

有时候需要接收任意数量的实参，但预先不知道传递给函数的会是什么信息，这种情况下，可将函数编写成能够接收任意数量的键值对

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--

def build_profile(first,last,**user_info):
    profile = {}
    profile['first_name'] = first
    profile['last_name'] = last
    for key,value in user_info.items():
        profile[key] = value
    return profile
user_profile = build_profile('albert','dinstein',
                             location = 'princeton',
                             field = 'physics')
print(user_profile)

 将函数存储在模块中

1:导入整个模块

pizza.py

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--
def make_pizza(size,*toppings):
print("\nMaking a " + str(size) +
"-inch pizza with the following toppings:")
for topping in toppings:
print("- " + topping)

在pizza.py目录下创建making_pizzas.py

#!/usr/bin/env python
# --*-- encoding:utf-8 --*--

import pizza

pizza.make_pizza(16,'pepperoni')
pizza.make_pizza(12,'mushrooms','green peppers','extra cheese')

Making a 16-inch pizza with the following toppings:
- pepperoni

Making a 12-inch pizza with the following toppings:
- mushrooms
- green peppers
- extra cheese

执行结果

2:导入特定的函数：

from module_name import function_name

通过用逗号分隔函数名，可根据需要从模块中导入任意数量的函数：

from module_nmae import function_0,function_1,function_2

from pizza import make_pizza

make_pizza(16,'pepperoni')

若使用这种语法，调用函数时就无需使用句点。由于在import语句中显式地导入了函数make_pizza()，因此调用它是只需指定起名字

3:使用AS给函数指定别名

from module_name import function_name as fn

from pizza import make_pizza as mp

mp(16,'pepperoni')

4.使用as给模块指定别名

import pizza as p

p.make_pizza(16,'pepperoni')

5:导入模块中的所有函数

from module_name import *

import语句中的星号让Python将模块pizza中的每个函数都复制到这个程序文件中。由于导入了每个函数，可通过名称来调用每个函数，而无需使用句点表示法。但可能出现模块中的函数名与本项目中使用的名称相同。

最佳的做法是：妖魔只导入你需要使用的函数，要么导入整个模块并使用句点表示法。

函数编写指南

1:给函数，模块指定描述性名称，且只在其中使用小写字母和下划线

2：每个函数应包含简要地阐述其功能的注释，该注释莹紧跟在函数定义后面，并采用文档字符串格式。

3：给形参制定默认值，等号两边不要有空格：

def function_name(parameter_0,parameter_1='default value')

对于函数调用中的关键字实参，也可遵循这种约定：

function_name(value_0,parameter='value')