[Python知识库]python字符串的方法

python字符串的方法

# capitalize 字符串首字母大写
s = "hello world!"
res = s.capitalize()
print(res)  # Hello world!

# title 每个单词的首字母大写 (非字母隔开的单词)
s = "xiao ming"
res = s.title()
print(res)  # Xiao Ming
ss = "xiao20ming"   # 用数字隔开
res = ss.title()
print(res)  # Xiao20Ming

# upper 将所有字母变成大写
s = "da xie"
res = s.upper()
print(res)  # DA XIE

# lower 将所有字母变成小写
s = "XIAO Xie"
res= s.lower()
print(res)  # xiao xie

# swapcase 大小写互换
s = "HU huan"
res = s.swapcase()
print(res)  # hu HUAN

# count 统计字符串中某个元素的数量
s = "fdjzdcdsssjcdhkxnashzd"
res = s.count("s")  # 默认从索引0开始统计
print(res)  # 4
res = s.count("s",15)  # 从索引15处开始统计
print(res)  # 1
res = s.count("s",0,9)  # 在索引0-8之间统计 [0,9)是一个左闭右开区间
print(res)  # 2

# find 查找某个字符串第一次出现的索引位置
s = "01234560123456"
res = s.find("1")    # 默认从索引0开始查找
print(res)  # 1
res = s.find("1",3)    # 默认从索引3开始查找
print(res)  # 8
res = s.find("1",3,6)    # 在索引3-6之间查找 [3,6)是一个左闭右开区间
print(res)  # -1  没有返回-1

# index 与 find 功能相同 find找不到返回-1,index找不到数据直接报错
s = "01234560123456"
res = s.index("2")
print(res)  # 2
# res = s.index("9")
# print(res) # ValueError: substring not found  ，报错

# startswith 判断是否以某个字符或字符串为开头
s = "hello woeld!"
res = s.startswith("he")    # 默认从索引0开始判断
print(res)  # True
res = s.startswith("he",2)    # 从索引2开始判断
print(res)  # False
res = s.startswith("he",0,1)    # # 在索引0-1之间判断 [0,1)是一个左闭右开区间
print(res)  # False


# endswith 判断是否以某个字符或字符串结尾,用法和startswith一样
s = "hello woeld"
res = s.endswith("ld")
print(res) # True
res = s.endswith("ld",-1)
print(res) # False
res = s.endswith("ld",-5,-1)
print(res) # False

# split 按某字符将字符串分割成列表(默认从左到右按空格分割,返回一个列表)
s = "a b c d e"
res = s.split() # 默认空格分割
print(res)  # ['a', 'b', 'c', 'd', 'e']
s = "a+b+c+d+e"
res = s.split("+")  # 用+号分割,结果没有分割字符
print(res)  # ['a', 'b', 'c', 'd', 'e']
res = s.split("+",2)  # 用+号分割,分割两次
print(res)  # ['a', 'b', 'c+d+e']

# join  将列表拼接成字符串(容器类型都可)
ls = ['0','1','2','3','4','5','6']
res = ''.join(ls)   # 默认无缝拼接，列表元素必须是字符串
print(res)  # 0123456
res = '+'.join(ls)   # 用+号拼接
print(res)  # 0+1+2+3+4+5+6

# replace 替换字符串(第三个参数选择替换的次数)
s = "a1 b1 c1 a2 b2 c2 a1 a1"
res = s.replace("a1","aa")  # 将所有的a1都转换成aa
print(res)  # aa b1 c1 a2 b2 c2 aa aa
# 第三个参数指定转换的次数
res = s.replace("a1","aa",1)  # 将一个a1转换成aa
print(res)  # aa b1 c1 a2 b2 c2 a1 a1

# isupper 判断字符串是否都是大写字母
s = "AABB"
ss = "Ab"
print(s.isupper())  # True
print(ss.isupper()) # False

# islower 判断字符串是否都是小写字母
s = "ab"
ss = "Ab"
print(s.islower())  # True
print(ss.islower()) # False

# splitlines 按换行来进行切分(\n)
s = '111\n222'
print(s.splitlines())   # ['111', '222']

# zfill  填充字符串(默认填充0,原字符串右对齐)
s = "哈哈"
print(s.zfill(10))  # 00000000哈哈

# ljust  填充字符串,原字符居左 (默认填充空格)
s = "哈哈"
print(s.ljust(20,"*"))  # 哈哈******************

# rjust  填充字符串,原字符居右 (默认填充空格)
s = "哈哈"
print(s.rjust(20,"+"))  # ++++++++++++++++++哈哈

# center 填充字符串,原字符居中 (默认填充空格)
s = "哈哈"
print(s.center(20,"-")) # ---------哈哈---------