1.1

定义函数：

def greet_user():

　　print (‘Hello the world‘)

执行函数： greet_user()

向函数传递参数：

def greet_user(username):

　　print (‘Hello,‘ + username.title() + ‘!‘ )           .title()  首字母大写

greet_user(‘lucy‘)                         执行时括号里添加参数

def describe_pet(animal_type,pet_name):
‘‘‘显示宠物的信息‘‘‘
print("\nI have a " + animal_type + ‘.‘)
print("My " + animal_type + " name is " + pet_name.title() + ‘.‘)

describe_pet(‘hamster‘,‘harry‘)

describe_pet(‘dog‘,‘while‘)                                       调用先后顺序不能错

def describe_pet(animal_type,pet_name):

print(‘\n I have a ‘ + animal_type + ‘.‘)

describe_pet(animal_type=‘hamster‘,pet_name=‘dog‘)                   关键字实参

1.2 默认值

编写函数时，可给每个形参制定默认值。调用函数时，给形参提供实参时，python将使用指定的实参，否则，将使用形参的默认值。

def greet_user(username=‘lucy‘):
print (‘hello‘)
greet_user()

2.1返回值

def get_formatted_name(first_name,last_name):
full_name = first_name + ‘ ‘ + last_name
return full_name.title()                                                  return将full_name 的值返回给函数get_formatted_name

musician = get_formatted_name(‘zn‘,‘zjy‘)

print(musician)    

2.2 让实参变成可选的

def get_formatted_name(first_name,last_name,middle_name=‘‘):
if middle_name:
full_name = first_name + ‘ ‘ + middle_name + ‘ ‘ + last_name

else:
full_name = first_name + ‘ ‘ + last_name

return full_name.title()

musician = get_formatted_name(‘zn‘,‘zzz‘)
print(musician)
musician = get_formatted_name(‘zn‘,‘zzx‘,‘zjy‘)
print(musician)

3.1返回字典

函数可返回任何类型的值，包括列表和字典等比较复杂的数据结构

def build_person(first_name,last_name):
person = {‘first‘:first_name,‘last‘:last_name}
return person

musician = build_person(‘zn‘,‘zzx‘)
print(musician)

def build_person(first_name,last_name,age):
person = {‘first‘:first_name,‘last‘:last_name}
if age:
person[‘age‘] = age
return person

mulition = build_person(‘zn‘,‘zzx‘,‘29‘)
print(mulition)

结合使用函数和while循环：

def get_formatted_name(first_name,last_name):
full_name = first_name + ‘ ‘ + last_name
return full_name.title()

while True:
print(‘\nPlease tell your name:‘)
print("enter ‘q‘ at any time to quit")

f_name = input(‘first name:‘)
if f_name ==‘q‘:
break

l_name = input(‘last name:‘)
if l_name == ‘q‘:
break

formatted_name = get_formatted_name(f_name,l_name)
print(‘\nHello,‘ + formatted_name + ‘!‘)

传递任意数量的实参：

def make_pizza(*toppings):
print(toppings)

make_pizza(‘pepperoni‘)
make_pizza(‘zxc‘,‘dsa‘,‘das‘)               函数只有一个形参*topping，不管提供多少个实参，这个形参豆浆它们统统收入囊中

形参名*topping中的星号让python创建一个名为topping的空元祖，并将值封装到这个元祖中

def make_pizza(*toppings):
print(‘\nMaking a pizza with the following toppings:‘)
for topping in toppings:
print ("-" + topping)
make_pizza(‘pep‘)
make_pizza(‘5‘,‘4‘,‘3‘,‘2‘,‘1‘)

2017-5-16 函数