Python笔记（蟒蛇书）_蟒蛇书电子版

1.起步（略）

Python一直没太学好，现在有机会了一定要自己来一遍和大佬们一起学习

2.字符串变量

简单的示例程序：

一定要动手写

变量名字只能包含字母、数字、下划线!

只能以字母或者下划线打头，不能以数字打头，变量名不能包含空格

2.1赋值字符串并打印：

message = "I am learning Python"
print(message)
message = "We are learning Englishi as well"
print(message)
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2.2使用字符串方法修改字符串大小写

name = 'richard lu'
print(name.title())	# 将字符串对象每个单词第一个字母大写
print(name.upper())	# 将字符串对象每个单词都大写
print(name.lower())	# 将字符串对象每个单词都小写
# 不会改变源字符串的内容
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2.3在字符串中使用变量: f 字符串

first_name = "ada"
last_name = "lovelace"
full_name = f"{first_name} {last_name}"
print(full_name.title())
print(f"Hello {full_name.title()}!")
# 要在字符串中插入变量的值，可在前引号前加上字母 f ,再将要插入的变量放在花括号内。这样，当Python 显示字符串时，将把每个变量都替换为其值

# 还可以使用f字符串来创建消息，再把整个消息赋给变量
message = f"Hello {full_name.title()}!"`
print(message)`

print(f"\t {message}")`
print("languages:\nPython\nC\nJavascript")`
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2.4利用strip()方法消除字符串末尾空格

favorite_language = 'Python '
print(favorite_language.rstrip())
favorite_language = favorite_language.rstrip()
print(favorite_language)
# strip()方法消除两边的空格
# lstrip()方法消除前面的空格
# rstrip()方法消除后面的空格
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3.列表[]

3.1 列表（个人理解就是数组，但是同时能装不同类型的）

bicycles = ['trek', 'cannonade', 'redline', 'specialized']
print(bicycles)
print(bicycles[-1].title())
message = f"My first vehicle is a {bicycles[0].title()}!"
print(message)
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3.2列表的修改、添加和删除元素

# 修改列表元素
bicycles[0] = 'bike'
print(bicycles)

# 添加列表元素（单引号和双引号在这里都可以，不做区分）
bicycles.append("car")
print(bicycles)

# 在列表中插入新的元素
bicycles.insert(0, "train")
print(bicycles)

# 在列表中删除特定下标的元素
del bicycles[0]
print(bicycles)

# 使用方法pop()删除元素
# pop()删除列表末尾的元素，并让你能够接着使用它。
popped_motorcycle = bicycles.pop()
print(popped_motorcycle)
print(bicycles)
print(f"I'd like to have a new {popped_motorcycle.title()}!")

# 根据列表中的值删除元素
bicycles.remove("car")
print(bicycles)

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3.3组织列表

# 使用方法sort()对列表进行永久排序
cars = ['bmw', 'audi', 'toyota', 'subaru']
cars.sort()
print(cars)
cars.sort(reverse=True) # 逆序
print(cars)

# 使用函数sorted()对列表临时排序
print("original list:")
print(cars)

print("sorted list")
print(sorted(cars))

print("original list")
print(cars)

# 列表逆置
cars.reverse()
print(cars)

# 确定列表的长度
print(len(cars))
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4.操作列表

4.1遍历整个列表

# for循环
magicians = ['alice', 'david', 'carolina']
for magician in magicians:
    print(f"{magician.title()}, that was a great trick!")
    print(f"I can't wait to see your next show {magician.title()}!\n")
print("Thank you, everyone. That was a great magic show!")
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4.2 创建数值列表

# 使用函数range() 经典差一思想 即输出1234
for value in range(1, 5):
    print(value)
# 使用range()创建数值列表
numbers = list(range(1, 6))
print(numbers)
even_numbers = list(range(2, 11, 2)) # range()可以指定步长
print(even_numbers)

# 创建1-10的平方的列表
squares = []
for value in range(1, 11):
    squares.append(value ** 2)
print(squares)

# 对数字列表执行简单的统计计算
digits = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
print(min(digits))
print(max(digits))
print(sum(digits))

# 列表解析：将for循环和创建新元素的代码合并成一行，并自动附加新元素
squares = [value ** 2 for value in range(1, 11)]
print(squares)
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4.3 使用列表的一部分

# 切片:仍然是一个列表
players = ['charles', 'martina', 'michael', 'florence', 'eli']
print(players[0:3])
print(players[1:4])
print(players[:4])
print(players[2:])
print(players[-3:])
# 遍历切片
print("Here are the first three players on my team：")
for player in players[:3]:
    print(player.title())
# 复制列表(两个列表各自占有各自的内存空间)

my_foods = ['pizza', 'felafel', 'carrot cake']
friend_foods = my_foods[:]

print("My favorite foods are:")
print(my_foods)

print("\nMy friend's favorite foods are:")
print(friend_foods)

my_foods.append("shit")
friend_foods.append("rice")

print("My favorite foods are:")
print(my_foods)

print("\nMy friend's favorite foods are:")
print(friend_foods)


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# 错误示范：复制列表
my_foods = ['pizza', 'felafel', 'carrot cake']
friend_foods = my_foods
# 这种语法实际上是让Python将新变量friends_foods关联到已经与my_foods相关联的列表，因此这两个变量指向同一个列表。有鉴于此，当把'shit'添加到my_foods中时，他也将出现在friend_foods中。同样，虽然'ice rice'好像只被加入到了friend_foods中，但他也将出现在这两个列表中
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4.5 元组

列表适合存储在程序运行期间可能变化的数据集。列表是可以修改的

Python 将不能修改的值称为不可变的，而不可变的列表称为元组

元组看起来很像列表，但使用圆括号而非中括号来标识。定义元组后，就可以使用索引来访问其元素，就像访问列表元素一样

# 访问元组的值
dimensions = (200, 50)
print(dimensions)
print(dimensions[0])

#如果定义只包含一个元素的元组，必须在这个元素后面加上逗号
my_t = (3,)
print(my_t)

#遍历元组
for dimension in dimensions:
    print(dimension)
#修改元组变量

print("Original dimensions:")
for dimension in dimensions:
    print(dimension)

dimensions = (400, 100)
print("\nModified dimensions:")
for dimension in dimensions:
    print(dimension)
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5. if 语句

5.1 示例

# 简单的实例-----注意冒号的问题

cars = ['audi', 'bmw', 'subaru', 'toyota']
for car in cars:
    if car == 'bmw':
        print(car.upper())
    else:
        print(car.title())

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5.2 条件测试

requested_topping = 'mushrooms'
if requested_topping != 'anchovies':
    print("Hold the anchovies")
    
answer = 17
if answer != 43:
    print("That is not the correct answer.Please try again!")

# 检查特定值是否包含在列表之中

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5.3 if 语句

# 使用关键字 in / not in检查特定值是否包含在列表中
requested_toppings = ['mushrooms', 'onions', 'pineapple']
if 'mushrooms' in requested_toppings:
    print("Wow It's in it")
if 'pepperoni' not in requested_toppings:
    print("It's not in it")

banned_users = ['andrew', 'carolina', 'david']
user = 'marie'

if user not in banned_users:
    print(f"{user.title()}, you can post a response if you wish.")
    
# if-else结构：
age = 17
if age >= 18:
    print("You're old enough to vote!")
    print("Have you registered to vote yet?")
else:
    print("Sorry, you're too young to vote.")
    print("Please register to vote as soon as you turn 18!")

# if-elif-else结构：
if age < 4:
    print("Your admission cost is $0.")
elif age < 18:
    print("Your admission cost is $25.")
else:
    print("Your admission cost is $40.")
# 简洁版
if age < 4:
    price = 0
elif age < 18:
    price = 25
else:
    price = 40
print(f"Your admission cost is ${price}.")
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5.4 使用if语句处理列表

requested_toppings = ['mushrooms', 'green peppers', 'extra cheese']
for requested_topping in requested_toppings:
    if requested_topping == 'green peppers':
        print("Sorry, we are out of green peppers right now")
    else:
        print(f"Adding {requested_topping}.")
print("\n Finished making your pizza")
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# 判断列表是否为空
requested_toppings = []
if requested_toppings:
    for requested_topping in requested_toppings:
        print(f"Adding {requested_topping}.")
    print("\nFinished making you pizza")
else:
    print("Are you sure you want a plain pizza?")
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# 两个列表交叉
available_toppings = ['mushrooms', 'olives', 'green peppers',
                      'pepperoni', 'pineapple', 'extra cheese']
requested_toppings = ['mushrooms', 'french fries', 'extra cheese']
for requested_topping in requested_toppings:
    if requested_topping in available_toppings:
        print(f"Adding {requested_topping}")
    else:
        print(f"Sorry, we don't have {requested_topping}")
print("\nFinished making your pizza.")
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6. 字典

6.1 一个简单的字典

# 这里应该是不区分大小写的
alien_0 = {"color": "green",
           "points": 5}
print(alien_0["color"])
print(alien_0["points"])

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6.2 使用字典

# 在字典中新加入键值对
alien_0["x_position"] = 0
alien_0["y_position"] = 25
print(alien_0)

# 日常使用时，可以先定义空的字典，再通过逻辑一步一步加入新的键值对
alien_0 = {}
alien_0['color'] = 'green'
alien_0['points'] = 5
print(alien_0)

# 修改字典中的值
alien_0['color'] = 'yellow'
print(f"The alien is now {alien_0['color']}.")

# 加入了if判断的小综合
alien_0 = {'x_position': 0,
           'y_position': 25,
           'speed': 'medium'}
print(f"Original position: {alien_0['x_position']}")

# 向右移动外星人
# 根据当前速度确定将外星人向右移动多远
if alien_0['speed'] == 'slow':
    x_increment = 1
elif alien_0['speed'] == 'medium':
    x_increment = 2
else:
    #这个外星人的移动速度肯定很快
    x_increment = 3
alien_0['x_position'] = alien_0['x_position'] + x_increment
print(f"New position: {alien_0['x_position']}")

# 删除键值对 注意：删除的键值对会永远消失

alien_0 = {'color': 'green', 'points': 5}
print(alien_0)

del alien_0['points']
print(alien_0)

# 由类似对象组成的字典：可以比较方便的去获取每个人的信息
favorite_language = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}
print(favorite_language)
language = favorite_language['sarah'].title()
print(f"Sarah's favorite labguage is {language}.")

# 使用get()来访问值
alien_0 = {'color': 'green',
           'speed': 'slow'}
# get()的第一个参数用于指定键，是必不可少的；第二个参数为指定的键不存在时要返回的值，是可选的
point_value = alien_0.get('points', 'No point value assigned')
print(point_value)

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6.3 遍历字典

# 遍历所有键值对
user_0 = {
    'username': 'efermi',
    'first': 'enrico',
    'last': 'fermi',
}

for key, value in user_0.items():
    print(f"\nKey: {key}")
    print(f"Value: {value}")

for name, language in favorite_language.items():
    print(f"{name.title()}'s favorite language is {language.title()}")

# 遍历字典中的所有键
# 方法keys()返回一个列表，其中包含字典中的所有键
friends = ['phil', 'sarah']
for name in favorite_language.keys():
    print(f"Hi {name.title()}.")
    if name in friends:
        language = favorite_language[name].title()
        print(f"\t{name.title()}, I see you love {language}!")

if 'erin' not in favorite_language:
    print("Erin, please take our poll!")
    
# 遍历字典中的所有值
# 通过对包含重复元素的列表调用set(),可以让Python找出列表中独一无二的元素，并使用这些元素来创建一个集合
print("The following languages have been mentioned:")
for language in set(favorite_language.values()):
    print(language.title())
    
# 可以使用一对花括号直接创建集合，并在其中用逗号分隔元素
# 集合和字典很容易混淆，因为他们都是用一对花括号定义的。当花括号内没有键值对时，定义的很可能是集合。不同于列表和字典，集合不会以特定的顺序存储元素

languages = {'python', 'ruby', 'python', 'c'}
print(languages)

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6.4 嵌套

# 字典列表（将字典嵌套在列表之中）


alien_0 = {'color': 'green', 'position': 5}
alien_1 = {'color': 'yellow', 'position': 10}
alien_2 = {'color': 'red', 'position': 15}
aliens = [alien_0, alien_1, alien_2]
for alien in aliens:
    print(alien)

# 创建一个用于存储外星人的空列表
aliens = []

# 创建30个绿色的外星人
for alien_number in range(0, 30):
    new_alien = {'color': 'green', 'points': 5, 'speed': 'slow'}
    aliens.append(new_alien)
# 显示前5个外星人
for alien in aliens[0:5]:
    print(alien)
print("...")

# 显示创建了多少个外星人
print(f"Total number of aliens: {len(aliens)}")

for alien in aliens[:3]:
    if alien['color'] == 'green':
        alien['color'] = 'yellow'
        alien['speed'] = 'medium'
        alien['points'] = 10
    elif alien['color'] == 'yellow':
        alien['color'] = 'red'
        alien['speed'] = 'fast'
        alien['points'] = 15
for alien in aliens[:5]:
    print(alien)
print("...")


# 在字典中存储列表
# 存储pizza信息
pizza = {
    'crust': 'thick',
    'toppings': ['mushrooms', 'extra cheese'],
}

# 概述所点的披萨
print(f"You ordered a {pizza['crust']}-crust pizza "
      "with the following toppings:")

for topping in pizza['toppings']:
    print("\t" + topping)

# 在字典中存储字典
users = {
    'aeinstein': {
        'first': 'albert',
        'last': 'einstein',
        'location': 'princeton',
    },
    'mcurie': {
        'first': 'marie',
        'last': 'curie',
        'location': 'paris',
    }
}
for username, user_info in users.items():
    print(f"\nUsername: {username}")
    full_name = f"{user_info['first']} {user_info['last']}"
    location = user_info['location']

    print(f"\tFull name: {full_name.title()}")
    print(f"\tLocation: {location.title()}")

``
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