《Python编程从入门到实践》第四章_操作列表

我会带着你远行 2022-05-15 04:24 269阅读 0赞

**for循环遍历整个列表**

注意点：

编写for循环的时候，对于用于存储列表中每个值的临时变量，可以指定任何名称，最好是选择有意义的；

python根据缩进来判断代码行与前一个代码行的关系，同一个缩进的代码属于同一个等级；

不要遗漏for语句后的冒号:

** 函数range()可以轻松生成一系列的数字**

注意，只打印到你指定的第二个值后停止。使用range()，如果输出不符号预期，请尝试将指定的值加一或者减一。

## 创建数字列表 ##

可以将range()的输出结果输入到函数list()中，直接转换为列表。

## 将1-10的平方的值加到一个列表里面去 ##

##  列表解析 ##

要使用这种语法，首先指定一个描述性的列表名，如squares；然后指定一个左方括号，并定义一个表达式

# 4.1 遍历整个列表
    magicians = ['alice', 'david', 'carolina']
    for magician in magicians:
        print(magician)
        # 4.1.2 在for循环中执行更多的操作
        print(magician.title() + ", that was a great trick!")
        print("I cant't wait to see you next trick," + magician.title() + ".\n")
    # 在for循环后面 没有缩进的代码都只执行一次
    # python通过使用缩进让代码更容易读
    print("Thank you,everyone.That was a great magic show!")
    
    # 4.2 避免缩进错误
    # 4.2.1 忘记缩进
    magicians = ['alice', 'david', 'carolina']
    # for magician in magicians:
    # print(magician)
    # IndentationError: expected an indented block
    # 通常,将紧跟for语句后面的代码行缩进 可消除这种缩进错误
    # 4.2.2 忘记缩进额外的代码行
    for magician in magicians:
        print(magician.title() + ", that was a great trick")
    print("I cant't wait to see your next trick,"+ magician.title() +".\n")
    # 4.2.3 不必要的缩进
    message = "Hello Python world"
    #   print(message)  IndentationError: unexpected indent
    # 只有要在for循环中对每个元素执行的代码需要缩进
    # 4.2.4 循环后不必要的缩进
    for magician in magicians:
        print(magician)
        # 4.1.2 在for循环中执行更多的操作
        print(magician.title() + ", that was a great trick!")
        print("I cant't wait to see you next trick," + magician.title() + ".\n")
        print("Thank you,everyone.That was a great magic show!")
    print("4.2.5 遗漏了冒号")
    # for magician in magicians
    #     print(magician)  SyntaxError: invalid syntax
    print("4.3 创建数值列表")
    print("4.3.1 使用函数range()")
    # range()函数让python从你指定的第一个值开始数 并到达你指定的第二个值后停止 因此输出不会包含第二个值
    for value in range(1,5):
        print(value)
    for value in range(1,6):
        print(value)
    print("4.3.2 使用函数range()创建数字列表 可使用函数list将range()的结果直接转换成列表")
    numbers = list(range(1, 6))
    print(numbers)
    # 使用函数range函数 还可指定步长
    even_numbers = list(range(2, 11, 2))
    print(even_numbers)
    # 创建一个列表 其中包含前10个整数的平方呢
    squares = []
    for value in range(1, 11):
        square = value ** 2   # 两个**表示乘方运算
        squares.append(square)
    print(squares)
    squares = []
    for value in range(1, 11):
        # 两个**表示乘方运算
        squares.append(value ** 2)  # 在循环中 计算每个值的平方 并立即将结果附加到列表的末尾
    print(squares)
    print("4.3.3 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))
    print("列表解析")
    squares = [value**2 for value in range(1, 11)]
    print(squares)
    #######################################################################################
    输出：
    C:\Anaconda3\python.exe H:/python/venv/text
    alice
    Alice, that was a great trick!
    I cant't wait to see you next trick,Alice.
    
    david
    David, that was a great trick!
    I cant't wait to see you next trick,David.
    
    carolina
    Carolina, that was a great trick!
    I cant't wait to see you next trick,Carolina.
    
    Thank you,everyone.That was a great magic show!
    Alice, that was a great trick
    David, that was a great trick
    Carolina, that was a great trick
    I cant't wait to see your next trick,Carolina.
    
    alice
    Alice, that was a great trick!
    I cant't wait to see you next trick,Alice.
    
    Thank you,everyone.That was a great magic show!
    david
    David, that was a great trick!
    I cant't wait to see you next trick,David.
    
    Thank you,everyone.That was a great magic show!
    carolina
    Carolina, that was a great trick!
    I cant't wait to see you next trick,Carolina.
    
    Thank you,everyone.That was a great magic show!
    4.2.5 遗漏了冒号
    4.3 创建数值列表
    4.3.1 使用函数range()
    1
    2
    3
    4
    1
    2
    3
    4
    5
    4.3.2 使用函数range()创建数字列表 可使用函数list将range()的结果直接转换成列表
    [1, 2, 3, 4, 5]
    [2, 4, 6, 8, 10]
    [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
    [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
    4.3.3 对数字列表执行简单的统计计算
    0
    9
    45
    列表解析
    [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
    
    Process finished with exit code 0

** 切片**

要创建切片，可指定要使用的第一个元素和最后一个元素的索引。**与函数range()一样，Python在到达你指定的第二个索引前面的元素后停止。**

可以是用for循环来遍历切片的数据

可以是索引\[:\]来复制列表，如果简单的使用等于号来将一个列表赋值给另一个列表，可以理解为这两个列表都指向的是同一个列表空间，改变其中一个列表就会改变另一个。

# 4.4使用列表的部分元素-切片
    print("4.4.1 切片")
    players = ['charles', 'martina', 'michael', 'florence', 'eli']
    print(players[0:3])
    
    players = ['charles','martina','michael','eli']
    print(players[1:])  # 如果没有指定最后一个位置，则一直切到尾部
    
    # 如果没有指定第一个索引 python将自动从列表开头开始提取
    players = ['charles', 'martina', 'michael', 'eli']
    print(players[:3])
    # 负数索引返回离列表末尾相应距离的元素
    players = ['charles', 'martina', 'michael', 'eli']
    print(players[-2:])
    
    print("4.4.2 遍历切片")
    players = ['charles', 'martina', 'michael', 'eli']
    print("Here are the first three players on my team:")
    for player in players[:3]:
        print(player.title())
    print(players[:3]) # 与函数range()一样 在到达指定的第二个索引前面的元素后停止
    print("可以是用for循环来遍历切片的数据")
    players = ['charles', 'martina', 'michael', 'eli']
    for player in players[1:4]:
        print(player)
    print("4.4.3 复制列表")
    my_foods = ['pizza', 'falafel', 'carrot cake']
    friend_food = my_foods[:]
    print("My favorite foods are:")
    print(my_foods)
    print("My friend's foods are:")
    print(friend_food)
    # 可以是索引[:]来复制列表，如果简单的使用等于号来将一个列表赋值给另一个列表，
    # 可以理解为这两个列表都指向的是同一个列表空间，改变其中一个列表就会改变另一个。
    my_foods = ['pizza', 'falafel', 'carrot cake']
    friend_foods = my_foods
    my_foods.append('cannoli')
    friend_foods.append('ice cream')
    print("My favorite foods are:")
    print(my_foods)
    print("My friend's favorite foods are:")
    print(friend_foods)
    #####################################################################################
    C:\Anaconda3\python.exe H:/python/venv/text
    4.4.1 切片
    ['charles', 'martina', 'michael']
    ['martina', 'michael', 'eli']
    ['charles', 'martina', 'michael']
    ['michael', 'eli']
    4.4.2 遍历切片
    Here are the first three players on my team:
    Charles
    Martina
    Michael
    ['charles', 'martina', 'michael']
    可以是用for循环来遍历切片的数据
    martina
    michael
    eli
    4.4.3 复制列表
    My favorite foods are:
    ['pizza', 'falafel', 'carrot cake']
    My friend's foods are:
    ['pizza', 'falafel', 'carrot cake']
    My favorite foods are:
    ['pizza', 'falafel', 'carrot cake', 'cannoli', 'ice cream']
    My friend's favorite foods are:
    ['pizza', 'falafel', 'carrot cake', 'cannoli', 'ice cream']
    
    Process finished with exit code 0

**元组 **

元组使用圆括号来标识，元组里面的元素不可增删，不可直接赋值修改！

可以是用for循环来遍历整个元组

虽然不能修改元组的元素，但可以给存储元组的变量赋值，因此，如果要修改，只能重新定义整个元组。

# 4.5 元组
    # 4.5.1 定义元组
    dimensions = (200, 50)
    print(dimensions[0])
    print(dimensions[1])
    # TypeError: 'tuple' object does not support item assignment
    # dimensions[0] = 250  由于试图修改元组的操作是被禁止的
    # 4.5.2 遍历元组中的所有值
    for dimension in  dimensions:
        print(dimension)
    print("4.5.3 修改元组的变量")
    dimensions = (200, 50)
    print("Original dimensions:")
    for dimension in dimensions:
        print(dimension)
    # 如果要修改前述矩阵的尺寸大小 可重新定义整个元组
    dimensions = (200, 50)
    print("Modifed dimensions:")
    for dimension in dimensions:
        print(dimension)
    ####################################################################
    C:\Anaconda3\python.exe H:/python/venv/text
    200
    50
    200
    50
    4.5.3 修改元组的变量
    Original dimensions:
    200
    50
    Modifed dimensions:
    200
    50
    
    Process finished with exit code 0