Python chapter 8 learning notes

定义一个函数

For example,

def greet_user():#定义函数

print("Hello!")

Now, we just need to input greet_user() and Hello! will be shown on the screen.

o   向函数传递信息

其实这一点和C语言基本是一致的。这个函数其实就是一个子函数，可以通过括号中的参数向子函数传递信息。

例子：

# -*-coding: utf-8 -*-

def greet_user(username):

 

print("Hello!" + username.title())

 

name = input("Please input your name.\n")

greet_user(name)

在这里面，形参就是指子函数def greet_user(username)括号里面的，实参就是最后一行里面的name所代表的。

o   关键字实参

def describe_pets(animal_type, pet_name):

print("\nI have a " + animal_type + ".")

print("My " + animal_type + "'s name is " + pet_name.title() + ".")

describe_pets(animal_type = 'cat', pet_name = 'hurry')#关键字实参

关键字实参的顺序无关紧要。但是普通的顺序必然非常重要。

o   默认值

def describe_pets(pet_name, animal_type = 'dog'):#默认值设置

print("\nI have a " + animal_type + ".")

print("My " + animal_type + "'s name is " + pet_name.title() + ".")

#typ = input("Please input the type of your pet.\n")

#name = input("Please input its name.\n")

 

#describe_pets(typ,name)

describe_pets(pet_name = 'hurry')#关键字实参

设置了默认值之后，默认值项得在形参括号中的最后。设置默认值之后，如果该参数不再修改，那么这个参数就自动为默认值，但是如果后面对其进行了传递，则使用传递的值而不再是默认值。设置了默认值之后，实参可以少一个（本例中，实参只剩1个）

·        返回值

o   返回简单值。此处返回值与C语言中类似。

o   让实参变成可选。可以利用指定一个默认值，即为空值即可。用到就在后面实参里写上，用不着就直接用默认的空。

o   返回字典。例如，

def build_person(first_name, last_name):

person = {'first': first_name,'last': last_name}

return person

musician = build_person('jimi', 'hendrix')

print(musician)

·        传递列表

o   在函数中修改列表

For example,

def print_models(unprinted_designs, completed_models):

while unprinted_designs:

current_design = unprinted_designs.pop()

print("Printing model: " + current_design)

completed_models.append(current_design)

Finally, unprinted_designs will not have any element. But, what if we want to retain these elements? The answer is as followed:

Use slice. function_name(list_name[:]).

For example, when we call function print_models(unprinted_designs, completed_models),we need to change it to print_models(unprinted_designs[:], completed_models).

·        Pass lots of actual parameter

o   Using *name as a formal parameter, this is just like a list.. For example,

def make_pizza(*toppings):

print(toppings)

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

o   Using **name as a formal parameter, this is just like a dict.

·        Import functions(★★★★★)

o   Import whole function

For example,

import pizza #There is a function file called pizza.py

pizza.make_pizza(16, 'pepperoni') # We need to point out the function from which file

o   Import specific function

from module_name import function_name

If we use this, we do not need to point out the function from which file.

·         Using as to specifying aliases for functions(用as为函数指定别名)/using as to specifying aliases for module（用as为模块指定别名）/import all functions from module.

o   from pizza import make_pizza as mp

o   import pizza as p

o   from pizza import *