Python list 常用操作

最后更新于：2022-03-27 01:12:23

Python list 常用操作

Python list 常用操作 Python3 实例

1.list 定义

实例

>>> li = ["a", "b", "mpilgrim", "z", "example"]
>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘z’, ‘example’]
>>> li[1]        
‘b’

2.list 负数索引

实例

>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘z’, ‘example’]
>>> li[–1]
‘example’
>>> li[–3]
‘mpilgrim’
>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘z’, ‘example’]
>>> li[1:3]  
[‘b’, ‘mpilgrim’]
>>> li[1:-1]
[‘b’, ‘mpilgrim’, ‘z’]
>>> li[0:3]  
[‘a’, ‘b’, ‘mpilgrim’]

3.list 增加元素

实例

>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘z’, ‘example’]
>>> li.append("new")
>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘z’, ‘example’, ‘new’]
>>> li.insert(2, "new")
>>> li
[‘a’, ‘b’, ‘new’, ‘mpilgrim’, ‘z’, ‘example’, ‘new’]
>>> li.extend(["two", "elements"])
>>> li
[‘a’, ‘b’, ‘new’, ‘mpilgrim’, ‘z’, ‘example’, ‘new’, ‘two’, ‘elements’]

4.list 搜索

实例

>>> li
[‘a’, ‘b’, ‘new’, ‘mpilgrim’, ‘z’, ‘example’, ‘new’, ‘two’, ‘elements’]
>>> li.index("example")
5
>>> li.index("new")
2
>>> li.index("c")
Traceback (innermost last):
 File "<interactive input>", line 1, in ?
ValueError: list.index(x): x not in list
>>> "c" in li
False

5.list 删除元素

实例

>>> li
[‘a’, ‘b’, ‘new’, ‘mpilgrim’, ‘z’, ‘example’, ‘new’, ‘two’, ‘elements’]
>>> li.remove("z")  
>>> li
[‘a’, ‘b’, ‘new’, ‘mpilgrim’, ‘example’, ‘new’, ‘two’, ‘elements’]
>>> li.remove("new")    # 删除首次出现的一个值
>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘example’, ‘new’, ‘two’, ‘elements’]    # 第二个 ‘new’ 未删除
>>> li.remove("c")     #list 中没有找到值, Python 会引发一个异常
Traceback (innermost last):
 File "<interactive input>", line 1, in ?
ValueError: list.remove(x): x not in list
>>> li.pop()      # pop 会做两件事: 删除 list 的最后一个元素, 然后返回删除元素的值。
‘elements’
>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘example’, ‘new’, ‘two’]

6.list 运算符

实例

>>> li = [‘a’, ‘b’, ‘mpilgrim’]
>>> li = li + [‘example’, ‘new’]
>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘example’, ‘new’]
>>> li += [‘two’]        
>>> li
[‘a’, ‘b’, ‘mpilgrim’, ‘example’, ‘new’, ‘two’]
>>> li = [1, 2] * 3
>>> li
[1, 2, 1, 2, 1, 2]

7.使用join链接list成为字符串

实例

>>> params = {"server":"mpilgrim", "database":"master", "uid":"sa", "pwd":"secret"}
>>> ["%s=%s" % (k, v) for k, v in params.items()]
[‘server=mpilgrim’, ‘uid=sa’, ‘database=master’, ‘pwd=secret’]
>>> ";".join(["%s=%s" % (k, v) for k, v in params.items()])
‘server=mpilgrim;uid=sa;database=master;pwd=secret’

join 只能用于元素是字符串的 list; 它不进行任何的类型强制转换。连接一个存在一个或多个非字符串元素的 list 将引发一个异常。

8.list 分割字符串

实例

>>> li = [‘server=mpilgrim’, ‘uid=sa’, ‘database=master’, ‘pwd=secret’]
>>> s = ";".join(li)
>>> s
‘server=mpilgrim;uid=sa;database=master;pwd=secret’
>>> s.split(";")  
[‘server=mpilgrim’, ‘uid=sa’, ‘database=master’, ‘pwd=secret’]
>>> s.split(";", 1)
[‘server=mpilgrim’, ‘uid=sa;database=master;pwd=secret’]

split 与 join 正好相反, 它将一个字符串分割成多元素 list。

注意, 分隔符 (“;”) 被完全去掉了, 它没有在返回的 list 中的任意元素中出现。

split 接受一个可选的第二个参数, 它是要分割的次数。

9.list 的映射解析

实例

>>> li = [1, 9, 8, 4]
>>> [elem*2 for elem in li]   
[2, 18, 16, 8]
>>> li
[1, 9, 8, 4]
>>> li = [elem*2 for elem in li]
>>> li
[2, 18, 16, 8]

10.dictionary 中的解析

实例

>>> params = {"server":"mpilgrim", "database":"master", "uid":"sa", "pwd":"secret"}
>>> params.keys()
dict_keys([‘server’, ‘database’, ‘uid’, ‘pwd’])
>>> params.values()
dict_values([‘mpilgrim’, ‘master’, ‘sa’, ‘secret’])
>>> params.items()
dict_items([(‘server’, ‘mpilgrim’), (‘database’, ‘master’), (‘uid’, ‘sa’), (‘pwd’, ‘secret’)])
>>> [k for k, v in params.items()]
[‘server’, ‘database’, ‘uid’, ‘pwd’]
>>> [v for k, v in params.items()]
[‘mpilgrim’, ‘master’, ‘sa’, ‘secret’]
>>> ["%s=%s" % (k, v) for k, v in params.items()]
[‘server=mpilgrim’, ‘database=master’, ‘uid=sa’, ‘pwd=secret’]

11.list 过滤

实例

>>> li = ["a", "mpilgrim", "foo", "b", "c", "b", "d", "d"]
>>> [elem for elem in li if len(elem) > 1]
[‘mpilgrim’, ‘foo’]
>>> [elem for elem in li if elem != "b"]
[‘a’, ‘mpilgrim’, ‘foo’, ‘c’, ‘d’, ‘d’]
>>> [elem for elem in li if li.count(elem) == 1]
[‘a’, ‘mpilgrim’, ‘foo’, ‘c’]

Python list 常用操作 Python3 实例