本文实例总结了Python实现list反转的方法。分享给大家供大家参考。具体实现方法如下:
下面有几个不同实现的函数
import math
def resv(li):
new = []
if li:
cnt = len(li)
for i in range(cnt):
new.append(li[cnt-i-1])
return new
def resv2(li):
li.reverse()
return li
def resv3(li):
hcnt = int(math.floor(len(li)/2))
tmp = 0
for i in range(hcnt):
tmp = li[i]
li[i] = li[-(i+1)]
li[-(i+1)] = tmp
return li
li = [1,2,3,4,5]
print resv(li)
def resv(li):
new = []
if li:
cnt = len(li)
for i in range(cnt):
new.append(li[cnt-i-1])
return new
def resv2(li):
li.reverse()
return li
def resv3(li):
hcnt = int(math.floor(len(li)/2))
tmp = 0
for i in range(hcnt):
tmp = li[i]
li[i] = li[-(i+1)]
li[-(i+1)] = tmp
return li
li = [1,2,3,4,5]
print resv(li)
ps: resv2() 方法会改变原来list的排序,其它则不会
一些关于list基础用法
1.定义list
>>> li = ["a","b","mpilgrim","z","example"]
>>> li
['a','b','mpilgrim','z','example']
>>> li[0]
'a'
>>> li[4]
'example'
>>> li
['a','b','mpilgrim','z','example']
>>> li[0]
'a'
>>> li[4]
'example'
2.负的list 索引
>>> li
['a','example']
>>> li[-1]
'example'
>>> li[-3]
'mpilgrim'
>>> li
['a','example']
>>> li[1:3]
['b','mpilgrim']
>>> li[1:-1]
['b','z']
>>> li[0:3]
['a','mpilgrim']
['a','example']
>>> li[-1]
'example'
>>> li[-3]
'mpilgrim'
>>> li
['a','example']
>>> li[1:3]
['b','mpilgrim']
>>> li[1:-1]
['b','z']
>>> li[0:3]
['a','mpilgrim']
3.向 list 中增加元素
>>> li
['a','example']
>>> li.append("new")
>>> li
['a','example','new']
>>> li.insert(2,"new")
>>> li
['a','new','new']
>>> li.extend(["two","elements"])
>>> li
['a','two','elements']
['a','example']
>>> li.append("new")
>>> li
['a','example','new']
>>> li.insert(2,"new")
>>> li
['a','new','new']
>>> li.extend(["two","elements"])
>>> li
['a','two','elements']
4.搜索 list
>>> li
['a','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
['a','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.从 list 中删除元素
>>> li
['a','elements']
>>> li.remove("z")
>>> li
['a','elements']
>>> li.remove("new")
>>> li
['a','elements']
>>> li.remove("c")
Traceback (innermost last):
File "<interactive input>",in ?
ValueError: list.remove(x): x not in list
>>> li.pop()
'elements'
>>> li
['a','two']
['a','elements']
>>> li.remove("z")
>>> li
['a','elements']
>>> li.remove("new")
>>> li
['a','elements']
>>> li.remove("c")
Traceback (innermost last):
File "<interactive input>",in ?
ValueError: list.remove(x): x not in list
>>> li.pop()
'elements'
>>> li
['a','two']
remove 从 list 中删除一个值的首次出现。
remove 仅仅 删除一个值的首次出现。 在这里,'new' 在 list 中出现了两次,但 li.remove("new") 只删除了 'new' 的首次出现。
如果在 list 中没有找到值,Python 会引发一个异常来响应 index 方法。
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。
6.list 运算符
>>> li = ['a','mpilgrim']
>>> li = li + ['example','new']
>>> li
['a','new']
>>> li += ['two']
>>> li
['a','two']
>>> li = [1,2] * 3
>>> li
[1,1,2]
>>> li = li + ['example','new']
>>> li
['a','new']
>>> li += ['two']
>>> li
['a','two']
>>> li = [1,2] * 3
>>> li
[1,1,2]
7.使用join链接list成为字符串
>>> 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 in params.items()])
'server=mpilgrim;uid=sa;database=master;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 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.分割字符串
>>> li = ['server=mpilgrim','pwd=secret']
>>> s = ";".join(li)
>>> s
'server=mpilgrim;uid=sa;database=master;pwd=secret'
>>> s.split(";")
['server=mpilgrim','pwd=secret']
>>> s.split(";",1)
['server=mpilgrim','uid=sa;database=master;pwd=secret']
>>> s = ";".join(li)
>>> s
'server=mpilgrim;uid=sa;database=master;pwd=secret'
>>> s.split(";")
['server=mpilgrim','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
>>> li = [1,9,8,4]
>>> [elem*2 for elem in li]
[2,18,16,8]
>>> li
[1,4]
>>> li = [elem*2 for elem in li]
>>> li
[2,8]
>>> [elem*2 for elem in li]
[2,18,16,8]
>>> li
[1,4]
>>> li = [elem*2 for elem in li]
>>> li
[2,8]
10.dictionary中的解析
>>> params = {"server":"mpilgrim","pwd":"secret"}
>>> params.keys()
['server','uid','database','pwd']
>>> params.values()
['mpilgrim','sa','master','secret']
>>> params.items()
[('server','mpilgrim'),('uid','sa'),('database','master'),('pwd','secret')]
>>> [k for k,v in params.items()]
['server','pwd']
>>> [v for k,v in params.items()]
['mpilgrim','secret']
>>> ["%s=%s" % (k,'pwd=secret']
>>> params.keys()
['server','uid','database','pwd']
>>> params.values()
['mpilgrim','sa','master','secret']
>>> params.items()
[('server','mpilgrim'),('uid','sa'),('database','master'),('pwd','secret')]
>>> [k for k,v in params.items()]
['server','pwd']
>>> [v for k,v in params.items()]
['mpilgrim','secret']
>>> ["%s=%s" % (k,'pwd=secret']
11.列表过滤
>>> li = ["a","foo","c","d","d"]
>>> [elem for elem in li if len(elem) > 1]
['mpilgrim','foo']
>>> [elem for elem in li if elem != "b"]
['a','foo','c','d','d']
>>> [elem for elem in li if li.count(elem) == 1]
['a','c']
>>> [elem for elem in li if len(elem) > 1]
['mpilgrim','foo']
>>> [elem for elem in li if elem != "b"]
['a','foo','c','d','d']
>>> [elem for elem in li if li.count(elem) == 1]
['a','c']
希望本文所述对大家的Python程序设计有所帮助。