字符串
定义:以单引号或双引号括起来的任意文本
#创建字符串
str1 = 'sunck is a good man!'
字符串运算
#字符串连接
str2 = 'sunck is a'
str3 = 'good man'
str4 = str2 +str3
print(str4)
#输出重复的字符串
str5 = 'good'
str6 = str5 *3
print('str6 =',str6)
#访问字符串中的某个字符
#通过索引下标查找字符,索引从0开始
str7 = 'sunck is a good man!'
print(str7[1])
#截取字符串中的一部分
#从给定下标处截取到给定下标之前
str8 = str7[:5]
#从给定下标处开始截取到结尾
str9 = str7[5:]
#判断某字符串是否在另一字符串中
print("good" in str7)
print("good1" not in str7)
格式化输出
#格式化输出
print("sunc is a good man")
num = 10
str10 = "sunck is a nice man!"
f = 10.1267
print("num =", num, "str10 =", str10)
# %d %s %f 占位符
# %.3精确到小数点后3位,会四舍五入
print("num = %d, str19 = %s, f = %.3f" % (num, str10, f))
# \\结果只现实一个\,第一个作为转义字符
print("sunck \\ is")
# \' \",不然外面要用三引号
print('tom is a \'good\' man')
print("tom is a \"good\" man")
#如果字符串内有很多换行,用\n写在一行不好阅读
#可用三引号保留字符串的格式
print("good\nnice\nhandsome")
print('''
good
nice
handsome
''')
#制表符 \t
print("sunck\tgood")
#如果字符中有好多字符串都需要转义,就需要加入好多\,
# 为了简化,Python允许用r表示内部的字符串默认不转义
# \\\t\\
print("\\\t\\") #结果 ‘\ \’
print(r"\\\t\\") #结果 ‘\\\t\\’
print(r"C:\Users\xlg\Desktop\Python-1704\day03") #结果 ‘C:\Users\xlg\Desktop\Python-1704\day03’
print("C:\\Users\\xlg\\Desktop\\Python-1704\\day03") #结果‘C:\Users\xlg\Desktop\Python-1704\day03’
'''
不同的操作系统的路径表示方法
windows
C:\\Users\\xlg\\Desktop\\Python-1704\\day03
linux
/root/user/sunck/Desktop/Python-1704/day03
'''
其他字符串中常用方法
#eval(str)
#功能:将字符串str当成有效的表达式来求值并返回计算结果
num1 = eval("123")
print(num1) #123
print(type(num1)) #int
print(eval("+123")) #123
print(eval("-123")) #-123
print(eval("12+3")) #15
print(eval("12-3")) #9
a123 = 234
print(eval("a123")) #234
#print(eval("12a3")) #报错
#len(str)
#返回字符串的长度(字符个数),空格,汉字都占一个字符
print(len("sunckisagoodman")) #输出15
print(len("sunck is a good man")) #输出19
print(len("sunck is a good man凯")) #输出20
#lower()转换字符串中大写字母为小写字母
str20 = "SUNCK is a Good Man!凯"
str21 = str20.lower()
print(str21)
print("str20 = %s" %(str20))
#upper()转换字符串中小写字母为大写字母
str21 = "SUNCK is a Good Man!"
print(str21.upper())
#swapcase()转换字符串中小写字母为大写字母,大写字母为小写字母
str22 = "SUNCK is a gOOd mAn!"
print(str22.swapcase())
#capitalize() 首字母大写,其他小写
str23 = "SUNCK is a gOOd mAn!"
print(str23.capitalize())
#title()每个单的首字母大写
str24 = "SUNCK is a gOOd mAn!"
print(str24.title())
# character char
#center(width[, fillchar])
#返回一个指定宽度的居中字符串,fillchar为填充的字符串,默认空格填充
str25 = "kaige is a nice man"
print(str25.center(40,"*")) #输出 **********kaige is a nice man***********
#ljust(width[, fillchar])
#返回一个指定宽度的左对齐字符串,fllchar为填充字符,默认空格填充
str26 = "kaige is a nice man"
print(str26.ljust(40, "%")) #输出:kaige is a nice man%%%%%%%%%%%%%%%%%%%%%
#rjust(width[, fillchar])
#返回一个指定宽度的右对齐字符串,fllchar为填充字符,默认空格填充
str27 = "kaige is a nice man"
print(str26.rjust(40, "%")) #输出:%%%%%%%%%%%%%%%%%%%%%kaige is a nice man
#zfill(width)
#返回一个长度为width的字符串,原字符串右对齐,前面补0
str28 = "kaige is a nice man"
print(str28.zfill(40))
#count(str[,start][,end])
#返回字符串中strc出现的次数,可以指定一个范围,默认从头到尾
str29 = "kaige is a very very nice man"
print(str29.count("very",15, len(str29) )) #输出1
#find(str[, start][,end])
#从左向右检测str字符串是否包含在字符串中,可以指定范围,默认从头到尾。得到的是第一次出现的开始下标,没有返回-1
str30 = "kaige is a very very nice man"
print(str30.find("very")) #输出11
#没有时输出-1,而不报错
print(str30.find("good")) #输出-1
print(str30.find("very", 15, len(str30))) #输出16
#rfind(str[, start][,end])]
#从右向左检测
str30 = "kaige is a very very nice man"
print(str30.rfind("very")) #输出16
#print(str30.rfind("good")) #输出-1
print(str30.rfind("very", 0, 15)) #输出11
#index(str, start=0, end=len(str))
#根find()一样,只不过如果str不存在的时候回报一个异常
str31 = "kaige is a very very nice man"
#print(str31.index("good")) #报错:ValueError: substring not found
#rindex(str, start=0, end=len(str))
#根rfind()一样,只不过如果str不存在的时候回报一个异常
str32 = "kaige is a very very nice man"
print(str32.rindex("very"))
#lstrip()截掉字符串左侧指定的字符,默认为空格
str33 = "*******kaige is a nice man"
print(str33.lstrip("*")) #输出:kaige is a nice man
#rstrip()截掉字符串右侧指定的字符,默认为空格
str34 = "kaige is a nice man "
print(str34.rstrip(), "*") #输出:kaige is a nice man *
#strip()截掉所有指定的字符
str35 = "*******kaige is a nice man*********"
print(str35.strip("*")) #输出:kaige is a nice man
#ord()函数用来返回对应字符的ascii码
#chr()用来表示ascii码对应的字符他的输入时数字,可以用十进制,也可以用十六进制。
str36 = "a"
print(ord(str36)) #输出:97
str37 = chr(65)
print(str37) #输出:A
print (chr(0x61)) #输出:a
print(" " != " ") #输出:False