12.Python：字符串类型

# str类型

a = "SEPIA"     # a = str("SEPIA")

# 类型转换
# str可以把任意其他类型转换成字符串
res = str({"a": 1})
res1 = {"a": 1}

print(res, type(res))
print(res1, type(res1))

# 使用
# (1).按索引取值(正向取，反向取)：只能取
msg = "Hello world"
# 正向取
print(msg[0])
print(msg[4])
# 反向取
print(msg[-1])

# (2).切片
res = msg[0:5]
print(res)

# (3).步长
res = msg[0:5:2]    # 从第0位开始取到第4位，间隔为2位
print(res)
res = msg[:]        # 正向取全部
#    .反向步长
res = msg[5:0:-1]   # 从第5位开始取到第1位，间隔为1位
print(res)
res = msg[::-1]     # 反向取全部

#    .取长度
msg = "Hello world"
print(len(msg))

#    .判断字符串是否在一个大字符串中
x = "e"
# print("e" in msg)
print(x in msg)

#    .移除空白strip
msg = "    111 222     "
res = msg.strip()     # 默认去掉左右两侧的空格
print(msg)
print(res)

msg = "******111 222******"
res = msg.strip("*")  # 去掉左右两侧的*
print(msg)
print(res)

#    .切分split
# 把一个字符串按照某种分隔符进行切分，得到一个列表
info = "SEPIA 32 male"
res = info.split()      # 默认按照空格分割
print(res)

info = "SEPIA:32:male"
res = info.split(":", 1)   # 默认按照":"分割, 指定分割次数
print(res)

# ————————————————————————————
# 需要掌握的操作
# strip,lstrip,rstrip
msg = "****111 222****"
print(msg.strip("*"))       # 去掉两侧的"*"
print(msg.lstrip("*"))      # 去掉左边的"*"
print(msg.rstrip("*"))      # 去掉右边的"*"

# lower,upper
msg = "HELLO world"
print(msg.lower())          # 转换成小写
print(msg.upper())          # 转换成大写

# startswith,endswith
print("Hello world".startswith("Hello"))    # 判断是否以""为开头
print("Hello world".endswith("world"))      # 判断是否以""为结尾

# split,rsplit
info = "SEPIA:32:male"
res = info.split(":", 1)     # 从左到右分割, 指定分割次数
res1 = info.rsplit(":", 1)   # 从右到左分割, 指定分割次数
print(res)
print(res1)

# join
l1 = ["SEPIA", "32", "male"]
res = " ".join(l1)
print(res)

# replace
msg = "you can you up, no can no bb"
res = msg.replace("can", "CAN", 1)    # 替换前字符串，替换后字符串，替换次数
print(res)

# isdigit
# 判断是否为纯数字
age = "32"
print(age.isdigit())
print(int(age), type(int(age)))

# ————————————————————————————
# 需要了解的操作

# find
msg = "hello world"
res = msg.find("e")     # 找到所查找字符的位置,找不到时返回-1
print(res)

# index
msg = "hello world"
res = msg.index("e")    # 找到所查找字符的位置,找不到时报错
print(res)

# count
msg = "hello world"
res = msg.count("o")    # 查找出现的次数
print(res)

# center,ljust,rjust,zfill
print("SEPIA".center(20, "*"))  # 打印时居中并用*填充空白
print("SEPIA".ljust(20, "*"))   # 打印时左对齐并用*填充空白
print("SEPIA".rjust(20, "*"))   # 打印时右对齐并用*填充空白
print("SEPIA".zfill(20))        # 打印时右对齐并用0填充空白

# expandtabs
msg = "hello\tworld"
print(msg.expandtabs(2))        # 指定制表符为2

# capitalize, swapcase, title
print("hello world".capitalize())   # 首字母大写
print("HELLO world".swapcase())     # 大小写反转
print("HELLO world".title())        # 每个单词首字母大写

# is

num1 = b"4"
num2 = u"4"
num3 = "四"
num4 = "Ⅳ"
# isdigit识别数字
print(num1.isdigit())     # true
print(num2.isdigit())     # true
print(num3.isdigit())     # false
print(num4.isdigit())     # false

# isnumeric识别数字,只能识别num2,num3,num4
print(num2.isnumeric())     # true
print(num3.isnumeric())     # true
print(num4.isnumeric())     # true

# isdecimal识别数字,只能识别num2
print(num2.isdecimal())     # true
print(num3.isdecimal())     # false
print(num4.isdecimal())     # false

# -----------------------------------------
# is了解
# print("abc".islower())          # 判断小写
# print("ABC".isupper())          # 判断大写
# print("Abc Def".istitle())      # 判断首字母大写
# print("123".isalnum())          # 判断数字
# print("abc".isalpha())          # 判断字母
# print("   ".isspace())          # 判断空格
# print("abc".isidentifier())     # 判断名字是否合法