【python @ 小甲鱼网课】 P8字符串（3）判断

字符串（3）

• 判断
• • startswith()
  • • startswith("a")
    • startswith("a",start,end)
    • startswith(("a","b","c"),start,end) 元组
  • endswith()
  • istitle()
  • isupper()
  • islower()
  • isalpha()
  • isspace()
  • isprintable()
  • isdecimal & isdigit & isnumeric
  • isalnum()
  • isidentifier()
• 判断字符是否为python保留标识符(if while for ...)

判断

函数	含义
startswith()	判断指定字符、字符串、元组是否出现在字符串的开始位置
endswith()	判断指定字符、字符串、元组是否出现在字符串的结束位置
istitle()	判断是否字符串中每个开头都为大写，其他为小写
isupper()	判断是否都为大写
islower()	判断是否都为小写
isalpha()	判断是否都为字母
isspace()	判断是否为空白字符串
isprintable()	判断是否存在转义字符
isdecimal()	判断是否为数字
isdigit()	判断是否为数字
isnumeris()	判断是否为数字
isalnum()	判断字符串是否由字母和数字构成
isidentifier()	判断字符串是否为合法字符串

startswith() startswith(“a”)

x = "hello world"
print(x.startswith("h"))
print(x.startswith("H"))
print(x.startswith("hello"))

startswith(“a”,start,end)

x = "hello world"
print(x.startswith("e",1))
print(x.startswith("ello",1))

startswith((“a”,“b”,“c”),start,end) 元组

startswith不仅仅可以判断字符、字符串，也可以判断元组

x = "hello world"
if x.startswith(("a","b","h")):
    print("yes")
else:
    print("no")

---

endswith()

类比startswith，参数相同，只是一个判断开头一个判断结尾。

endswith(“a”) & endswith(“a”,start,end)

x = "hello world"
print(x.endswith("d"))
print(x.endswith("world"))
print(x.endswith("worl",0,-1))
print(x[-2])

---

istitle()

判断字符串是否为大小字母开头，其他字符为小写字符

x = "Hello World"
print(x.istitle())
x = "HEllo World"
print(x.istitle())
x = "Hello world"
print(x.istitle())

---

isupper()

判断字符串中是否所有字符都是大写

x = "Hello World"
print(x.isupper())
x = "HELLO WORLD"
print(x.isupper())
x = "HELLO WORLd"
print(x.isupper())

---

islower()

类比isupper()，islower()判断是否字符串中所有字符都为小写字符

x = "hello world"
print(x.islower())
x = "hello World"
print(x.islower())
x = "HELLO world"
print(x.islower())

---

isalpha()

判断字符串中是不是都是字母

x = "hello world"
print(x.isalpha())
x = "helloworld"
print(x.isalpha())
x = "hello1111"
print(x.isalpha())

第一个是 Flase 的原因是 hello 和 world 中间出现空格非字母

---

isspace()

判断字符串是否为空白字符串

x = "     nt"
print(x.isspace())

---

isprintable()

判断是否可以打印，主要是判断是否存在转义字符

x = "hello world"
print(x.isprintable())
x = "hello worldn"
print(x.isprintable())

---

isdecimal & isdigit & isnumeric

判断是否为数字，但是可以判断的范围不同

x = "12345"
print(x.isdecimal())
print(x.isdigit())
print(x.isnumeric())
x = "2²"
print(x.isdecimal())
print(x.isdigit())
print(x.isnumeric())
x = "Ⅰ"
print(x.isdecimal())
print(x.isdigit())
print(x.isnumeric())
x = "一二三四五"
print(x.isdecimal())
print(x.isdigit())
print(x.isnumeric())

---

isalnum()

集大成者，只要isalpha、isdecimal、isdigit、isnumeric中有一个为true则为true

---

isidentifier()

判断字符串是否为合法的标识符
合法：不可以数字开头，不存在空格…

x = "hello world"
print(x.isidentifier())
x = "hello_world"
print(x.isidentifier())
x = "520hello"
print(x.isidentifier())

---

判断字符是否为python保留标识符(if while for …)

import keyword
print(keyword.iskeyword("if"))
print(keyword.iskeyword("while"))
print(keyword.iskeyword("array"))