（Python基础教程之八）Python中的list操做

时间 2021-05-07

标签 python 编程数组 app 分布式函数 oop post 学习 spa 栏目 Python 繁體版

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在Python中，列表为：python

有序
索引（索引从0开始）
易变的
异构的（列表中的项目没必要是同一类型）
写为方括号之间的逗号分隔值列表

listOfSubjects = ['physics', 'chemistry', "mathematics"]
listOfIds = [0, 1, 2, 3, 4]
miscList = [0, 'one', 2, 'three']

1. Access list items

要访问列表中的值，请使用切片语法或数组索引形式的方括号来获取单个项目或项目范围。编程

传递的索引值能够是正数或负数。若是索引是负数则从列表的末尾开始计数。数组

list [m : n]表示子列表从索引m（包括）开始，到索引n（不包括）结束。app

若是m未提供，则假定其值为零。
若是n未提供，则选择范围直到列表的最后。

ids = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
print( ids[0] )            # 0
print( ids[1:5] )        # [1, 2, 3, 4]
print( ids[ : 3] )        # [0, 1, 2]
print( ids[7 : ] )        # [7, 8, 9]\
print( ids[-8:-5] )        # [2, 3, 4]

2. Modily list

要更改列表中的特定项目，请使用其索引引用该项目并分配一个新值。分布式

charList =  ["a", "b", "c"]
charList [2] = "d"
print (charList)    # ['a', 'b', 'd']

3. Iterate a list

咱们能够使用来遍历列表项for loop。函数

charList =  ["a", "b", "c"]

for x in charList:
    print(x)

# a
# b
# c

4. Check if a item exists in the list

使用'in'关键字肯定列表中是否存在指定的项目。oop

charList =  ["a", "b", "c"]
if "a" in charList:
    print("a is present")    # a is present

if "d" in charList:
    print("d is present")
else:
    print("d is NOT present")    # d is NOT present

5. Finding length of the list

使用该len()函数查找给定列表的长度。post

charList =  ["a", "b", "c"]
x = len (charList)
print (x)    # 3

6. Adding items

要将项目添加到列表的末尾，请使用append(item)方法。
要在特定索引位置添加项目，请使用insert(index, item)方法。若是index大于索引长度，则将项目添加到列表的末尾。

charList =  ["a", "b", "c"]
charList.append("d")    
charList.append("e")
print (charList)        # ['a', 'b', 'c', 'd', 'e']
charList.insert(5, "f")

print (charList)        # ['a', 'b', 'c', 'd', 'e', 'f']

charList.insert(10, "h")    # No error 

print (charList)    # ['a', 'b', 'c', 'd', 'e', 'f', 'h']

7. Removing items

若要从列表中删除项目，四个途径使用一个，即remove()，pop()，clear()或del关键字。学习

7.1. remove()

它经过其值删除指定的项目。spa

charList =  ["a", "b", "c"]
charList.remove("c")    
print (charList)        # ['a', 'b']

7.2. pop()

它经过索引删除指定的项目。若是未提供index，它将从列表中删除最后一项。

charList =  ["a", "b", "c", "d"]
charList.pop()            # removes 'd' - last item
print (charList)        # ['a', 'b', 'c']
charList.pop(1)            # removes 'b'
print (charList)        # ['a', 'c']

7.3. clear()

它清空列表。

charList =  ["a", "b", "c", "d"]
charList.clear()    
print (charList)        # []

7.4. del keyword

它能够用来从列表的索引中删除项目。咱们也能够使用它删除整个列表。

charList =  ["a", "b", "c", "d"]
del charList[0]    

print (charList)        # ['b', 'c', 'd']

del charList

print (charList)        # NameError: name 'charList' is not defined

8. Join two lists

咱们能够使用"+"运算符或extend()函数将两个给定的列表加入Python 。

charList = ["a", "b", "c"]
numList    = [1, 2, 3]

list1 = charList + numList

print (list1)    # ['a', 'b', 'c', 1, 2, 3]

charList.extend(numList)

print (charList)    # ['a', 'b', 'c', 1, 2, 3]

9. Python list methods

9.1. append()

在列表的末尾添加一个元素。

charList =  ["a", "b", "c"]

charList.append("d")

print (charList)    # ["a", "b", "c", "d"]

9.2. clear()

从列表中删除全部元素。

charList =  ["a", "b", "c"]

charList.clear()

print (charList)    # []

9.3. copy()

返回列表的副本。

charList =  ["a", "b", "c"]

newList = charList.copy()

print (newList)    # ["a", "b", "c"]

9.4. count()

返回具备指定值的元素数。

charList =  ["a", "b", "c"]

x = charList.count('a')

print (x)    # 1

9.5. extend()

将列表的元素添加到当前列表的末尾。

charList = ["a", "b", "c"]
numList    = [1, 2, 3]

charList.extend(numList)

print (charList)    # ['a', 'b', 'c', 1, 2, 3]

9.6. index()

返回具备指定值的第一个元素的索引。

charList =  ["a", "b", "c"]

x = charList.index('a')

print (x)    # 0

9.7. insert()

在指定位置添加元素。

charList =  ["a", "b", "c"]

charList.insert(3, 'd')

print (charList)    # ['a', 'b', 'c', 'd']

9.8. pop()

删除指定位置或列表末尾的元素。

charList =  ["a", "b", "c", "d"]

charList.pop()            # removes 'd' - last item

print (charList)        # ['a', 'b', 'c']

charList.pop(1)            # removes 'b'

print (charList)        # ['a', 'c']

9.9. remove()

删除具备指定值的项目。

charList =  ["a", "b", "c", "d"]

charList.remove('d')

print (charList)        # ['a', 'b', 'c']

9.10. reverse()

颠倒列表中项目的顺序。

charList =  ["a", "b", "c", "d"]

charList.reverse()

print (charList)        # ['d', 'c', 'b', 'a']

9.11. sort()

默认状况下，以升序对给定列表进行排序。

charList =  ["a", "c", "b", "d"]

charList.sort()

print (charList)        # ["a", "b", "c", "d"]

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做者：分布式编程
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