python之列表操作

1.列表的增操作（四种）

1. append（object）：append object to end，directly used on list
2.  insert（index，object）：insert object before index，directly used on list
3. extend（iterable object）：extend list by appending elements from the iterable，directly used on list
4.  "+"：拼接，list1 + list2 = [each elements in list1 and list2]

# 1.append
a.append([9,8,7,6])
print(a)
--[1, 2, 3, 4, 5, 6, [9, 8, 7, 6]]

# 2.insert
a.insert(7, 8)
print(a)
--[1, 2, 3, 4, 5, 6, [9, 8, 7, 6], 8]

# 3. extend
a.extend("zhang")
print(a)
--[1, 2, 3, 4, 5, 6, [9, 8, 7, 6], 8, 'z', 'h', 'a', 'n', 'g']

# 4. +
a = a+[9]
print(a)
--[1, 2, 3, 4, 5, 6, [9, 8, 7, 6], 8, 'z', 'h', 'a', 'n', 'g', 9]

2.列表的删操作（四种）

1. remove(value)：remove first occurrence of value, Raises ValueError if the value is not present.directly used on list
2. pop（index）：remove and return item at index (default last)，Raises IndexError if list is empty or index is out of range.directly used on list
3. del[start:end:step]：remove items chosen by index，directly used on list 
4. clear()：remove all items from list

a = [1, 2, 3, 4, 5, 6, 7, 8, 9]
# 1.remove
a.remove(3)
print(a)
--[1, 2, 4, 5, 6, 7, 8, 9]

# 2.pop
s = a.pop(1)
print(s)
print(a)
--2
--[1, 4, 5, 6, 7, 8, 9]

# 3. del
del a[0:4:2]
print(a)
--[4, 6, 7, 8, 9]

# 4. clear
a.clear()
print(a)
--[]

3.列表的改操作（两种）

　　直接利用 list[index] = object 修改，[index]可以按照切片的格式修改多个，切片的部分规则如下

1. 类似于replace（替换）方法，[ ]内选的值无论多少均删去，新修改的元素无论多少均插入list中
2. 当新元素只是一个单独的字符串时，将字符串分解为单个字符后全部加入列表

a = [1, 2, 3, 4, 5, 6, 7, 8, 9]
a[1:2] = "1", "2", "3"
print(a)
--[1, '1', '2', '3', 3, 4, 5, 6, 7, 8, 9]

a[1:3] = "1", "2", "3"
print(a)
--[1, '1', '2', '3', '3', 3, 4, 5, 6, 7, 8, 9]

a[1:4] = "1", "2"
print(a)
--[1, '1', '2', '3', 3, 4, 5, 6, 7, 8, 9]

a[1:2] = "come on"
print(a)
--[1, 'c', 'o', 'm', 'e', ' ', 'o', 'n', '2', '3', 3, 4, 5, 6, 7, 8, 9]

4.列表的查操作（两种）

• directly query with list[index]
• using for loop just like “for i in list ”，each i in loop is item in list. 

5.count(value)  

count(value):return number of occurrences of value

6.index(value)

return first index of value.Raises ValueError if the value is not present.

7.reverse()

reverse *IN PLACE*

8.sort(key=None, reverse=False)

stable sort *IN PLACE*, if reverse is True(default is False), sort from big to small.