Python学习笔记4—列表

Posted 2020-08-06 头痛不头痛

列表定义

>>> a=[‘Free‘,‘1998‘]
>>> type(a)
<type ‘list‘>
>>> bool(a)          #列表有值，则为true
True
>>> print a
[‘Free‘, ‘1998‘]
>>> 

索引和切片

>>> a=[‘Hello‘,‘World‘,‘2006‘]
>>> a[1]
‘World‘
>>> a[1:2]
[‘World‘]
>>> a[-2:-1]
[‘World‘]

list函数

>>> dir(list)
[‘__add__‘, ‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__delitem__‘, ‘__delslice__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__getitem__‘, ‘__getslice__‘, ‘__gt__‘, ‘__hash__‘, ‘__iadd__‘, ‘__imul__‘, ‘__init__‘, ‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__mul__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__reversed__‘, ‘__rmul__‘, ‘__setattr__‘, ‘__setitem__‘, ‘__setslice__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘append‘, ‘count‘, ‘extend‘, ‘index‘, ‘insert‘, ‘pop‘, ‘remove‘, ‘reverse‘, ‘sort‘]

appand 追加元素

>>> fruits=[‘orange‘,‘apple‘,‘banana‘]
>>> fruits.append(‘matermelon‘)
>>> fruits
[‘orange‘, ‘apple‘, ‘banana‘, ‘matermelon‘]

 extend 合并两个list

>>> a=[1,2,3]
>>> b=[4,5]
>>> a.extend(b)
>>> a
[1, 2, 3, 4, 5]

extend 的对象是一个 list，如果是 str，则 Python 会先把它按照字符为单位转化为 list 再追加到已知 list

>>> la = [1,2,3]
>>> b = "abc"
>>> la.extend(b)
>>> la
[1, 2, 3, ‘a‘, ‘b‘, ‘c‘]
>>> c = 5
>>> la.extend(c)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: ‘int‘ object is not iterable

 

reverse  反转

方法1[::-1]

>>> a=[1,2,3]
>>> a[::-1]
[3, 2, 1] 
>>> a="python"
>>> a[::-1]
‘nohtyp‘
>>> 

方法2：list(reversed(list))

>>> a=[1,2,3]
>>> list(reversed(a))
[3, 2, 1]

方法3：reverse

>>> a=[1,2,3]
>>> a.reverse()
>>> a
[3, 2, 1]

count  统计某一个元素在list中出现的次数，如果没有则返回0

>>> c=[a,b,c,a,a]
>>> c.count(a)
3
>>> c.count(‘f‘)
0

index 返回索引

>>> c=[a,b,c,a,a]
>>> c.index(a)         #第一次出现的位置
0

insert

list.insert(i, x) 中的 i 是将元素 x 插入到 list 中的位置，即将 x 插入到索引值是 i 的元素前面。注意，索引是从 0

>>> l=[‘a‘,‘b‘,‘c‘,‘d‘]
>>> l.insert(1,‘#‘)
>>> l
[‘a‘, ‘#‘, ‘b‘, ‘c‘, ‘d‘]

如果i大于索引的最大值，那么就变成追加了

>>> a = [1,2,3]
>>> a.insert(9,777)
>>> a
[1, 2, 3, 777]

remove 

移除掉第一次匹配的元素

>>> lst=[‘a‘,‘b‘,‘a‘,‘c‘]
>>> lst.remove(‘a‘)
>>> lst
[‘b‘, ‘a‘, ‘c‘]

pop

根据索引移除某一个元素

>>> lst=[‘a‘,‘b‘,‘a‘,‘c‘]
>>> lst.pop(0)
‘a‘
>>> lst
[‘b‘, ‘a‘, ‘c‘]

sort

默认情况，实现的是从小到大的排序。

>>> lst=[4,5,7,1,9]
>>> lst.sort()
>>> lst
[1, 4, 5, 7, 9]

从大到小

>>> lst=[4,5,7,1,9]
>>> lst.sort(reverse=True)
>>> lst
[9, 7, 5, 4, 1]

按照关键字排序

>>> lst = ["Python","java","c","pascal","basic"]
>>> lst.sort(key=len)
>>> lst
[‘c‘, ‘java‘, ‘basic‘, ‘Python‘, ‘pascal‘]