数据类型_列表

一、列表数据类型

“列表”是一个值，它包含多个字构成的序列。

spam = ["hello",3.14159,True,"elephant"]
[]

变量spam只被赋予值：列表值，但列表值本身包含多个值。

[]是一个空列表，不包含任何值，类似于空字符串“”。

• 用下表取得列表中的单个值：

spam = ['cat','bat','rat','elephant']
spam[0]
spam[1]
spam[2]
spam[3]

下标只能是整数，不能是浮点值

spam = ['cat','bat','rat','elephant']
>>> spam[1]
'bat'

spam[1.0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list indices must be integers or slices, not float

列表也可以包含其他列表值。这些列表的列表中的值，可以通过多下标来访问

spam = [["cat","bat"],[10,20,30,40,50]]
>>> spam[0]
['cat', 'bat']
>>> spam[0][1]
'bat'
>>> spam[1][4]
50

第一个下标表明使用哪个列表值，第二个下标表明该列表中的值

• 负数下标

虽然下标从0开始并向上增长，但也可以用负整数作为下标。

spam = ['cat','bat','rat','elephant']
>>> spam[-1]
'elephant'
>>> spam[-3]
'bat'

• 利用切片取得子列表

spam = ['cat','bat','rat','elephant']
spam[2]
spam[1:4]
spam[0:-1]

• 用len获取列表长度

spam=['cat','dog','hello']
len(spam)

• 用下标改变列表的值

spam=["dak","bat","rat","elephant"]
spam[1]="aardvark"
spam
['dak', 'aardvark', 'rat', 'elephant']
spam[-1]="ssfd"
spam
['dak', 'aardvark', 'rat', 'ssfd']

• 列表链接和列表复制

#列表连接
[1,2,3]+["a","B","c"]

#列表复制
["x","Y","z"] * 3

• 用del语句从列表中删除值

spam=["cat","bat","rat","elephant"]
del spam[2]
spam
["cat","bat","elephant"]

 二、使用列表

• 列表用于循环

supplies=["pens","staplers","flame-throwers","binders"]
for i in range(len(supplies)):
    print("Index " + str(i) +"in supplies is:" + supplies[i])

Index 0 in supplies is:pens
Index 1 in supplies is:staplers
Index 2 in supplies is:flame-throwers
Index 3 in supplies is:binders

• in 和 not in 操作符

>>> spam = ["hello","hi","howdy","heyas"]
>>> "cat" in spam
False
>>> "howdy"  in spam
True

• 多重赋值技巧

>>> cat = ["fat","black","loud"]
>>> size,color,disposition = cat
>>> cat
['fat', 'black', 'loud']

三、增强赋值操作

增强的赋值语句	等价的赋值语句
spam +=1	spam = spam + 1
spam -=1	spam = spam -1
spam *=1	spam = spam * 1
spam /=1	spam = spam/1
spam %=1	spam = spam%1

四、方法

• 用index()方法在列表中查找值

>>> spam = ["Zophie","Pooka","fat-tail","hello","sdfd","hello"]
>>> spam.index("hello")
3

• 用append()和insert()方法在列表中添加值

>>> spam = ["cat","dog","bat"]
>>> spam.append("sdfds")
>>> spam
['cat', 'dog', 'bat', 'sdfds']

>>> spam = ["cat","dog","bat"]
>>> spam.insert(1,"suning")
>>> spam
['cat', 'suning', 'dog', 'bat']

append()方法调用，将参数添加到列表末尾，insert()方法可以在列表任意下标处插入一个值。

• 用remove()方法从列表中删除值

>>> spam = ["cat","dog","bat","elephant"]
>>> spam.remove("bat")
>>> spam
['cat', 'dog', 'elephant']

• 用sort()方法将列表中的值排序

>>> spam = [2,5,3.14,1,-7]
>>> spam.sort()
>>> spam
[-7, 1, 2, 3.14, 5]
>>> spam.sort(reverse=True)
>>> spam
[5, 3.14, 2, 1, -7]
>>> spam = ['a',"z","A","Z"]
>>> spam.sort(key=str.lower)
>>> spam
['a', 'A', 'z', 'Z']