Python 编程从入门到实践3

8.1 定义函数

关键词:def

文档字符串: '''str'''

传递实参的方式:

        1.位置实参  

        2.关键字实参 

        3.默认值   

        4.混合使用

8.3.2 让实参变成可选

给实参指定一个默认值 - 空字符串,并将这个实参一道形参列表的末尾,这样可以使实参变成可选。

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()
    
    # 位置实参
musician = get_formatted_name('jimi', 'hendrix')
print(musician)
musician = get_formatted_name('john', 'hooker', 'lee')
print(musician)

 >>> Jimi Hendrix
 >>> John Lee Hooker
 >>> {'first_name': 'albert', 'last_name': 'einstein', 'location': 'princeton'}

8.3.4 结合使用函数和while循环

def get_formatted_name(first_name, last_name):
    '''返回整洁的姓名'''
    full_name = first_name + ' ' + last_name
    return full_name


while True:
    print("\nPlease tell me 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 + '!')

8.5传递任意数量的实参

def make_prizza(*toppings):
    print(toppings)

make_prizza('pepperoni')
make_prizza('mushrooms', 'green peppers', 'extra cheese')

 >>> ('pepperoni',)
 >>> ('mushrooms', 'green peppers', 'extra cheese')

8.5.2使用任意数量的关键字实参

将函数变成成能接受任意数量的键 - 值对

def build_profile(first, last, **urser_info):
    profile = {}
    profile['first_name'] = first
    profile['last_name'] = last
    for key, value in urser_info.items():
        profile[key] = value
        return profile


user_profile = build_profile('albert', 'einstein', location='princeton', field='physics')
print(user_profile)

>>> {'first_name': 'albert', 'last_name': 'einstein', 'location': 'princeton'}

9.1创建和使用类

class Dog():
    # __init__() 方法:每当一个类创建新实例时, python 都会自动运行它 
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def sit(self):
        # 模拟小狗被命令蹲下
        print(self.name.title() + 'is now sitting')
 

#9.1.2 根据类创建一个实例
my_dog = Dog('willie','6')
#访问属性
print(my_dog.name.title() + ',' +my_dog.age)
#调用方法
my_dog.sit()

>>> Willie,6
>>> Willieis now sitting

9.2.3修改属性的值

class Car():
    def __init__(self, make):
        self.make = make
        # 给属性指定默认值
        self.odmeter_reading = 0

    # 打印车辆信息
    def read(self):
        print('This ' + self.make.title() + ' has ' + str(self.odmeter_reading) + ' miles on it')

    def update_odometer(self, mileage):
        # 将里程表读数设置为指定的值
        self.odmeter_reading = mileage
  
my_new_car = Car('audi')
# 1.直接修改属性
my_new_car.odmeter_reading = 23
my_new_car.read()

# 2.通过方法修改属性
my_new_car.update_odometer(25)
my_new_car.read()

>>> This Audi has 23 miles on it
>>> This Audi has 25 miles on it

9.3继承

#括号中添加所要继承的父类
class ElectricCar(Car):
    # 电动汽车的独特之处
    def __init__(self, make):
        # 初始化父类的属性
        super().__init__(make)
        # 1.添加子类特有属性以及方法
        self.battery_size = 70

    def describe_battery(self):
        # 打印出电瓶容量的消息
        print('This ' + self.make.title() + ' has a ' + str(self.battery_size) + '-kwh battery.')
    #2.重写方法
    def read(self):
        print('这是一辆电动汽车')


my_tesla = ElectricCar('tesla')
my_tesla.read()

>>> 这是一辆电动汽车
>>> This Tesla has a 70-kwh battery.

10.1 从文件中获取数据

10.0.1 读取整个文件

with open('digits.txt')as file_object:
    # 逐行读取
    for line in file_object:
        # 每行末尾都有一个看不见的换行符,使用 rstrip() 去掉空行
        print(line.rstrip())
        # contents = file_object.read()
        # print(contents)

10.2 写入文件

with open('text.txt', 'w')as file_object:
    # w:写入模式 a:追加模式 r:读取模式 r+:可读可写模式
    file_object.write('I love python')
    # 注意 Python 只能将字符串写入文件文件,写入数字必须先使用 str() 将其转换为字符串

10.4存储数据

10.4.1 使用 json.dump() 和 json.load()

import json

numbers = [2, 3, 4]
filename = 'numbers.json'
with open(filename, 'w') as f_obj:
    # json.dump() 接受 2 个数据:1.数据 2.文件位置
    json.dump(numbers, f_obj)
 
# 使用json.load() 将列表读取到内存中
with open(filename) as f_obj:
    numbers = json.load(f_obj)
print(numbers)

综合使用

# 如果以前存储了用户名,就加载它
# 否则,就提示用户输入用户名并保存它
filename = 'username.json'
try:
    with open(filename) as f_obj:
        username = json.load(f_obj)
except FileNotFoundError:
    username = input('What is your name?')
    with open(filename, 'w') as  f_obj:
        json.dump(username, f_obj)
        print('we will remember you, ' + username + '!')
else:
    print('Welcome back, ' + username + '!')