python列表
2016-06-23 19:12
447 查看
一、列表的基本知识
列表的定义:
空列表:>>> [] #空的列表 [] >>> type([]) <type 'list'> >>> a = [] >>> bool(a) False >>>
**注意:**python的列表中的元素可以是任何python对象,可以是字典、集合、列表等等。
如下例子,列表中元素可以是任何对象:
>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> a ['laoshi', 25, 89.9, ['laoshi', 25, 89.9]]
列表的索引和切片:
简单取出:>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> a[0] #列表索引是从0开始的 'laoshi' >>> a[1] 25 >>> a[2] 89.9 >>> a[0:2] ['laoshi', 25] >>> a[:2] #[]中左边的值不写,表示从头开始 ['laoshi', 25] >>> a[0:] #[]中右边的值不写,意思就是到结尾为止 ['laoshi', 25, 89.9, ['laoshi', 25, 89.9]] >>>
从列表右边开始的话,-1 是第一个索引:
>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> a[-1] ['laoshi', 25, 89.9]
取出列表中的列表中的元素,例如:
>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> a[3] ['laoshi', 25, 89.9] >>> a[3][0] #相当于二维列表 'laoshi' >>>
获取的列表的索引,即下标,例如:
>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> a.index(25) 1 >>> a.index("laoshi") 0
列表的反转
第一种写法:>>> lst = [1,2,3,4,5,6] >>> lst[::-1] # -1是指步长为1,并代表反方向 [6, 5, 4, 3, 2, 1] >>> lst[0:4:2] # 0为起始值,4为末尾值,2为步长,并代表正方向 [1, 3] >>>
第二种写法:
>>> lst = [1,2,3,4,5,6] >>> list(reversed(lst)) [6, 5, 4, 3, 2, 1] >>>
列表的基本操作:
列表的长度 len 的操作,例如:>>> lst = [1,2,3,4,5,6] >>> len(lst) 6
”+“的加法操作,例如:
>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> lst = [1,2,3,4,5,6] >>> lst + a [1, 2, 3, 4, 5, 6, 'laoshi', 25, 89.9, ['laoshi', 25, 89.9]] >>>
“ * ”乘法的操作,作用是列表元素重复,例如:
>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> a*2 ['laoshi', 25, 89.9, ['laoshi', 25, 89.9], 'laoshi', 25, 89.9, ['laoshi', 25, 89.9]] >>>
in、max()、min()、cmp() 的操作,例如:
>>> a = ["laoshi",25,89.9,["laoshi",25,89.9]] >>> lst = [1,2,3,4,5,6] >>> 25 in a # ni的操作表示该元素是否在列表中 True >>> max(lst) 6 >>> min(lst) 1 >>> max(a) 'laoshi' >>> min(a) 25 >>> cmp(a,lst) 1 >>>
二、列表的常用函数
追加和扩展:append、Extend>>> 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'] >>>
append()的用法:
>>> help(list.append) Help on method_descriptor: append(...) L.append(object) -- append object to end >>>
举例如下:
>>> a = [1,2] >>> a.append(100) >>> a [1, 2, 100] >>> a.append(["google","facebook"]) >>> a [1, 2, 100, ['google', 'facebook']] >>>
extend()的用法:
>>> help(list.extend) Help on method_descriptor: extend(...) L.extend(iterable) -- extend list by appending elements from the iterable >>>
说明extend(iterable)中的iterable必须是可迭代的,这点重要。
举例如下:
>>> a = [1,2,3] >>> b = [4,5,6] >>> a.extend(b) >>> a [1, 2, 3, 4, 5, 6] >>> a.extend("python") #注意,此处字符串"python"是不可迭代的,但会将字符串中每个字符一个一个地取出,并输出。 >>> a [1, 2, 3, 4, 5, 6, 'p', 'y', 't', 'h', 'o', 'n'] >>> a.extend(5) # 5 不是可迭代的,所以会报如下错误 Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'int' object is not iterable >>>
可迭代的判断方法:
>>> b = [1,2] >>> hasattr(b,'__iter__') True >>> hasattr("python",'__iter__') False >>> hasattr(5,'__iter__') False >>>
append()和extend()的重要区别:
>>> a= [1,2] >>> a.append([4,5]) #append的用法 >>> a [1, 2, [4, 5]] >>> >>> >>> a = [1,2] >>> a.extend([4,5]) #extend的用法 >>> a [1, 2, 4, 5] >>>
其他函数,如Count()、Index()、Insert()、Pop()、Remove()、Reverse()、Sort()
Count()的用法:
>>> help(list.count) Help on method_descriptor: count(...) L.count(value) -> integer -- return number of occurrences of value >>>
count(value):表示value的值在列表中出现的次数,例如:
>>> a = [1,1,1,2,2,1] >>> a.count(1) 4 >>> a.count(2) 2
Index()的用法:
>>> help(list.index) Help on method_descriptor: index(...) L.index(value, [start, [stop]]) -> integer -- return first index of value. Raises ValueError if the value is not present. >>>
index(value)返回的是value所在的第一个索引值,例如:
>>> a [1, 1, 1, 2, 2, 1] >>> a.index(1) 0 >>> a.index(2) 3 >>>
Insert()的用法:
>>> help(list.insert) Help on method_descriptor: insert(...) L.insert(index, object) -- insert object before index >>>
举例如下:
>>> a = ["python","web"] >>> a.insert(1,"Xiaoxu") >>> a ['python', 'Xiaoxu', 'web'] >>> a.insert(0,20161111) >>> a [20161111, 'python', 'Xiaoxu', 'web'] >>>
Pop()的用法:
>>> help(list.pop) Help on method_descriptor: pop(...) L.pop([index]) -> item -- remove and return item at index (default last). Raises IndexError if list is empty or index is out of range. >>>
举例如下:
>>> a = [20161111, 'python', 'Xiaoxu', 'web'] >>> a.pop(2) 'Xiaoxu' >>>
Remove()的用法:
>>> help(list.remove) Help on method_descriptor: remove(...) L.remove(value) -- remove first occurrence of value. Raises ValueError if the value is not present. >>>
若有多个相同的值,remove()只能删除第一个值
举例如下:
>>> a = ["taishan","taishan","huangshan"] >>> a.remove("taishan") >>> a ['taishan', 'huangshan'] >>>
Reverse()的用法:
>>> help(list.reverse) Help on method_descriptor: reverse(...) L.reverse() -- reverse *IN PLACE* >>>
举例如下:
>>> a = [1,2,3,4] >>> a.reverse() >>> a [4, 3, 2, 1] >>>
Sort()的用法:
>>> help(list.sort) Help on method_descriptor: sort(...) L.sort(cmp=None, key=None, reverse=False) -- stable sort *IN PLACE*; cmp(x, y) -> -1, 0, 1 >>>
举例如下:
>>> a = [5,3,9,2] >>> a.sort() #默认的是升序排列 >>> a [2, 3, 5, 9] >>> >>> b = [5,3,9,2] >>> b.sort(reverse=True) #此处设置降序排列 >>> b [9, 5, 3, 2] >>>
相关文章推荐
- Python动态类型的学习---引用的理解
- Python3写爬虫(四)多线程实现数据爬取
- 垃圾邮件过滤器 python简单实现
- 下载并遍历 names.txt 文件,输出长度最长的回文人名。
- install and upgrade scrapy
- Scrapy的架构介绍
- Centos6 编译安装Python
- 使用Python生成Excel格式的图片
- 让Python文件也可以当bat文件运行
- [Python]推算数独
- Python中zip()函数用法举例
- Python中map()函数浅析
- Python将excel导入到mysql中
- Python在CAM软件Genesis2000中的应用
- 使用Shiboken为C++和Qt库创建Python绑定
- FREEBASIC 编译可被python调用的dll函数示例
- Python 七步捉虫法