String and related methods of Python data type introduction

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1、python String type of , keyword str; Definition ： Pairs of single and double quotation marks enclose the string

Be careful ：python Define variables in , Do not need to use variable type keywords ：str character string int integer float floating-point tuple Tuples dict Dictionaries list list

str_2="lemon python class "
str_1='PythonAotuTest'
print(type(str_1))
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2、 The value of the string , He is orderly , A string is composed of elements one by one , And there's an index index, from 0 Angle mark start number , It also supports reverse order from -1 Start

print(" Take the value of string variable ：",str_2)
print(" Positive values ：",str_2[2]," Reverse value ：",str_2[-16])
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3、 Special characters \n \t \r, escape Add... Before the string r/R Or backslash \, After the transfer is the ordinary string output \n

str_2=r"python\nclass" 
print(str_2)
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4、 String operations + Splicing ,* ride . priority ; Support the same type + Splicing ： Different types of splicing , Need to transform , Compulsive . That is, the original type is forced to be spliced with the same type

# print(str_2+str_1*4)
# i=(1,2,3)
# j=111
# print(str(j)+str_1)
# print(str(i)+str_1)
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5、 member operator ：in not in

print(" member operator , conditional ：",'i' not in str_2,'o' not in  str_2)
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6、 Slice value m:n:k The starting position ： Target location ： step ( Isochromatic ) The default is 1, Take left instead of right n-1 End value

# [:]  Take it from head to tail ,[2:] from 2 Start taking to the end  [::2] from 0 Start , The isochron is 2 Take to the tail ,[:7:] from 0 Fetch 7 The isochron is 1
print(" Slice value ：",str_2[1:16:3],", Support reverse order slicing :",str_2[-16:-3:1]) #  The reverse order is [-16:] Tolerable 
# print(str_2[::2])
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7、 Format output ,%s character string ( You can put any type of value ） %d Integers %f Floating point numbers ,%.2f Keep two decimal places

# %() Coercive transformation , commas , The order value is 
# format {} The space occupation can not mark the position , The default order value is ,index from 0 Start , If the index value , Just mark by index 
age=19
name='python'
print(" Format output ：{1}{0}".format(age,name),", Place holder :%s Output %s："%(str_2,age))
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8、 Use of built-in functions

#  Case Toggle ：upper()、lower()
print(" Capitalization :",str_2.upper()," A lowercase letter :",str_1.lower())
# swapcase() Capitalize interchangeably 
print(str_1.swapcase())
# find() Look for the element 
print(" Find the index of the element index:",str_2.find("t"),", Element index not found index Default return ：",str_1.find("3"))
#  Substitution function replace(), Be replaced , Replacement value , Specify how many times to replace 
print(str_1," Comparison before and after string element replacement :",str_1.replace("t","T",2))
# split()  function , Cut string , Return list type , The type of list element is still string 
str_4=str_2.split("n")
print(str_2," Comparison of string elements before and after cutting :",str_2.split("n"),", Type after cutting ：",type(str_4),
      ", But the elements inside \'{}\' Type or string ：".format(str_4[2]),type(str_4[2]))
# strip() Handle the character elements at the beginning and end 
print(str_2," Comparison of string elements before and after processing :",str_2.strip("l"))
#  Length function __len__()
print(" Return string str_2 The length of ：",str_2.__len__())
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