[Python] 字符串操作及方法总结

txt1 = 'Hello World!!'
print(txt1) # Hello World!!
txt2 = "Hello World!!"
print(txt2) # Hello World!!

str1 = 'What\'s your name?'
str2 = "What's your name?"
print(str1) # What's your name?
print(str2) # What's your name?

str1 = 'Hello'
str2 = 'World'
print(str1 + str2) # HelloWorld
print(str1 + ' ' + str2) # Hello World

txt = 'ABCDEFGHIJKLMN'
print(txt[0]) # A
print(txt[2]) # C
print(txt[-2]) # M
print(txt[-1]) # N

tag = 'Hudas Blog'
tag[9:36] # 'https://blog.csdn.net/Hudas'
tag[38:-4] # 'Hudas Blog'

txt = 'I love Python very much!!' 
print(len(txt)) # 25

exp_str = "Hello World!!"
result = exp_str.startswith("Hello")
print(result) # True

txt = "China is a great country"
result = txt.endswith("country")
# True
print(result)

txt = "hello world!!"
# 把所有字符中的小写字母转换成大写字母
print(txt.upper()) # HELLO WORLD!!
# 把所有字符中的大写字母转换成小写字母
print(txt.lower()) # hello world!!
# 把第一个字母转化为大写字母，其余小写
print(txt.capitalize()) # Hello world!!
# 把每个单词的第一个字母转化为大写，其余小写 
print(txt.title()) # Hello World!!
 
txt1 = "blog.csdn.net"
# BLOG.CSDN.NET
print(txt1.upper()) 
# blog.csdn.net
print(txt1.lower())
# Blog.csdn.net
print(txt1.capitalize()) 
# Blog.Csdn.Net
print(txt1.title())

str1 = 'Python'
str1.find('t') # 2
str1.index('t') # 2
str1.find('hon') # 3
str1.index('hon') # 3
str1.find('z') # -1
str1.index('z') # ValueError: substring not found

txt = 'This is a test'
# This is a demo
print(txt.replace('test','demo'))

sentence = "The lazy brown fox jumps over the lazy dog"
 
for words in (("brown", "red"), ("lazy", "quick")):
    sentence = sentence.replace(*words)
# The quick red fox jumps over the quick dog
print(sentence)

txt = "   Andy437   "
# 去除首尾空格 
print(txt.strip()) #Andy437
# 去除左边空格
print(txt.lstrip()) #Andy437
# 去除右边空格
print(txt.rstrip()) #   Andy437

txt = '1+2+3+4+5'
# ['1', '2', '3', '4', '5']
print(txt.split('+'))
 
txt1 = '/usr/bin/env'
# ['', 'usr', 'bin', 'env']
print(txt1.split('/'))
 
txt2 = 'Using the default'
# ['Using', 'the', 'default']
print(txt2.split())

nums = [1, 2, 3, 4, 5]
s = '+'
# 报错，TypeError: sequence item 0: expected str instance, int found
print(s.join(nums))

nums = ['1', '2', '3', '4', '5']
s = '+'
# '1+2+3+4+5'
print(s.join(nums))

# 检查字符'a'在sentence中出现的次数
sentence = 'Canada is located in the northern part of North America'
counter = sentence.count('a')
print(counter) # 6

# 检查字符'a'在sentence中出现的次数
sentence = 'Canada is located in the northern part of North America'
# 方法1
import re
counter = len(re.findall("a", sentence))
print(counter) # 6
 
# 方法2
from collections import Counter
counter = Counter(sentence)
print(counter['a']) # 6

# 下面输出结果都为"My name is Andy, I'am 18"
txt1 = "My name is {fname}, I'am {age}".format(fname = "Andy", age = 18)
txt2 = "My name is {0}, I'am {1}".format("Andy",18)
txt3 = "My name is {}, I'am {}".format("Andy",18)

txt1 = "python"
print(txt1.isalpha()) #True
 
# 中文的汉字会被isalpha判定为True
txt2 = "这是一个例子"
print(txt2.isalpha()) # True
# 如果想区分中文和英文，可以使用如下方法
print(txt2.encode("utf-8").isalpha()) # False
 
txt3 = "Andy安迪"
print(txt3.isalpha()) # True
print(txt3.encode("utf-8").isalpha()) # False

str1 = '123456'
print(str1.isdigit()) # True
 
str2 = "Hello Wrold!!"
print(str2.isdigit()) # False
 
str3 = '0'
print(str3.isdigit()) # True
 
str4 = '-1'
print(str4.isdigit()) # False
 
str5 = '1.437'
print(str5.isdigit()) # False
 
str6 = '12.0'
print(str6.isdigit()) # False

txt1 = "HELLO world!!!"
print(txt1.islower()) # False
txt2 = "hello world!!!"
print(txt2.islower()) # True
txt3 = '437'
print(txt3.islower()) # False
txt4 = 'andy437'
print(txt4.islower()) # True
txt5 = 'Andy437'
print(txt5.islower()) # False

txt1 = "HELLO WORLD!!!"
print(txt1.isupper()) # True
txt2 = "HELLO world!!!"
print(txt2.isupper()) # False
txt3 = '437'
print(txt3.isupper()) # False
txt4 = 'andy437'
print(txt4.isupper()) # False
txt5 = 'Andy437'
print(txt5.isupper()) # False
txt6 = 'ANDY437'
print(txt6.isupper()) # True

txt = 'Andy'
print(txt.istitle()) # True
txt1 = 'Aa Bc'
print(txt1.istitle()) # True
txt2 = 'Aa_Bc'
print(txt2.istitle()) # True
txt3 = 'Aa bc'
print(txt3.istitle()) # False
txt4 = 'Aa_bc'
print(txt4.istitle()) # False
txt5 = 'Aa BC'
print(txt5.istitle()) # False
txt6 = '437'
print(txt6.istitle()) # False
txt7 = 'A437'
print(txt7.istitle()) # True
txt8 = 'helloWorld'
print(txt8.istitle()) # False

txt1 = "   "
print(txt1.isspace()) # True
txt2 = "Test"
print(txt2.isspace()) # False
txt3 = "  Test  "
print(txt3.isspace()) # False
txt4 = ' \t'
print(txt4.isspace()) # True
txt5 = '\n'
print(txt5.isspace()) # True
txt6 = 'Aa Bb'
print(txt6.isspace()) # False

txt = ''
print(txt.isspace()) # False

username1 = ""
 
# 方法1:使用字符串长度判断
if len(username1) == 0:
    print("用户名不能为空")
 
# 方法2:使用==判断是否为空
if username1 == '':
    print("用户名不能为空")
 
# 方法3:直接判断是否为空
if username1:
    print("Welcome!!")
else:
    print("用户名不能为空")
 
username2 = " "
# 使用.isspace()判断是否字符串全部是空格
if username2.isspace() == True:
    print("用户名不能为空")