python String(字符串)

'''什么是字符串
字符串是以单引号或双引号括起来的任意文本
'abc'
"def"
字符串不可变
'''

#创建字符串
str1 = "sunck is a good man!"
str3 = "sunck is a nice man!"
str5 = "sunck is a handsome man!"

'''
字符串运算
'''
#字符串连接
str6 = "sunck is a "
str7 = "good man"
str8 = str6 + str7
print("str6 =", str6)
print("str7 =", str7)
print("str8 =", str8)
#输出重复字符串
str9 = "good"
str10 = str9 * 3
print("str10 =", str10)
#访问字符串中的某一个字符
#通过索引下标查找字符，索引从0开始
#字符串名[下标]
str11 = "sunck is a good man!凯"
print(str11[1])
#str11[1] = "a" #字符串不可变
print("str11 =", str11)

#截取字符串中的一部分
str13 = "sunck is a good man!"
#从给定下标出开始截取到给定下标之前
str15 = str13[6:15]
#从头截取到给定下标之前
str16 = str13[:5]
#从给定下标处开始截取到结尾
str17 = str13[16:]
print("str17 =", str17)

str18 = "sunck is a good man"
print("good" in str18)
print("good1" not in str18)

#print(~5)  #6
'''
00000101
11111010
10000110
'''

#格式化输出
print("sunc is a good man")
num = 10
str19 = "sunck is a nice man!"
f = 10.1267
print("num =", num, "str19 =", str19)
#  %d   %s   %f  占位符
#                                   精确到小数点后3位，会四舍五入
print("num = %d, str19 = %s, f = %.3f" % (num, str19, f))

'''
转义字符   \
将一些字符转换成有特殊含义的字符
'''
#\n
print("num = %d\nstr19 = %s\nf = %.3f" % (num, str19, f))
'''
\\
'''
print("sunck \\ is")

# \'   \"
print('tom is a \'good\' man')
print("tom is a \"good\" man")
#      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
print("good\nnice\nhandsome")
print('''
good
nice
handsome
''')

'''
\t   制表符
'''
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(r"\\\t\\")
print(r"C:\Users\xlg\Desktop\Python-1704\day03")
print("C:\\Users\\xlg\\Desktop\\Python-1704\\day03")
'''
windows
  C:\\Users\\xlg\\Desktop\\Python-1704\\day03
linux
  /root/user/sunck/Desktop/Python-1704/day03
'''


#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)
print(type(num1))
print(eval("+123"))
print(eval("-123"))
print(eval("12+3"))
print(eval("12-3"))
#print(eval("a123"))
#print(eval("12a3"))


#len(str)
#返回字符串的长度(字符个数)
print(len("sunck is a good man凯"))

#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,"*"))


#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, "%"))



#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, "%"))


#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) ))


#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"))
print(str30.find("good"))
print(str30.find("very", 15, len(str30)))


#rfind(str[, start][,end])]
str30 = "kaige is a very very nice man"
print(str30.rfind("very"))
#print(str30.rfind("good"))
print(str30.rfind("very", 0, 15))

#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"))


#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("*"))

#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(), "*")

str35 = "*******kaige is a nice man*********"
print(str35.strip("*"))


str36 = "a"
print(ord(str36))
str37 = chr(65)
print(str37)

print(" " != " ")