Python__list 常用操作

list常用操作：

1、list定义：

li = ["a","b","mpilgrim","z","example"]
print (li)
print (li[1])

2、list负数索引：

li = ["a","b","mpilgrim","z","example"]
print (li[-3])
print (li[1:3])
print (li[1:-1])
print (li[0:3])

3、list增加元素：

li = ["a","b","mpilgrim","z","example"]
li.append("new")    # 增加new
print (li)

li.insert(2,"new1")     # 将 new 增加到第2位
print (li)

li.extend(["two","elements"])
print (li)     # 增加 two, elements

4、list搜索：

li = ["a","b","mpilgrim","z","example"]
print (li.index("example"))

print (li.index("new"))

print (li.index("c"))   # 没有“c”,会报错

5、list删除元素：

li = ['a','b','new','mpilgrim','z','example','new','two','elements']
li.remove("z")   #删除z
print (li)

l2 = ['a','b','new','mpilgrim','example','new','two','elements']
l2.remove("new")  #删除首次出现的一个值new
print (l2)

l3 = ['a','b','mpilgrim','example','new','two','elements']
l3.remove("c")   #list中没有找到值，Python会引发一个异常
print (l3)

l3.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
print (l3)

6、list运算符：

li = ['a','b','mpilgrim']
li = li + ['example','new']   #增加“example”，“new”
print (li)

li += ['two']
print (li)    #增加“two”

l2 = [1,2] * 3   #输出3遍[1,2]
print (l2)

7、使用join链接list成为字符串：

# join只能用于元素时字符串的list；它不进行任何的类型强制转换。链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。
params = {"server":"mpilgrim","database":"master","uid":"sa","pwd":"secret"}
print (["%s=%s" % (k,v)for k,v in params.items()])
# ['server=mpilgrim', 'uid=sa', 'database=master', 'pwd=secret']

print ("；".join(["%s=%s" % (k,v)for k,v in params.items()]))
# 'server=mpilgrim;uid=sa;database=master;pwd=secret'

8、list分割字符串：

li = ['server=mpilgrim','uid=sa','database=master','pwd=secret']
s = "；".join(li)
print (s)

s1 = s.split("；")   #split将字符串分割成多元素list
print (s1)    #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

s2 = s.split(";",1)   #split接受一个可选的第二个参数，它是要分割的次数
print (s2)

9、list的映射解析：

li = [1,9,8,4]
li = [elem*2 for elem in li]
print (li)

10、dictionary中的解析：

params = {"server":"mpilgrim","database":"master","uid":"sa","pwd":"secret"}
print (params.keys())    # 取字典中的键
print (params.values())  # 取字典中的值
print (params.items())   # 将字典格式转换为列表

print ([k for k,v in params.items()])
print ([v for k,v in params.items()])
print (["%s=%s" % (k,v)for k,v in params.items()])

11、list过滤：

li = ["a","mpilgrim","foo","b","c","d","d"]

print ([elem for elem in li if len(elem) > 1])

print ([elem for elem in li if elem !="b"])

print ([elem for elem in li if li.count(elem) == 1])