Python strings

Python string is a built-in type text sequence. It is used to handle textual data in python. Python Strings are immutable sequences of Unicode points. Creating Strings are simplest and easy to use in Python.

We can simply create Python String by enclosing a text in single as well as double quotes. Python treat both single and double quotes statements same.

Example : 

a = "Hello"
b= 'ApkZube'
print(a+" "+b) 

output of above example  :

        Hello ApkZube
        

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Accessing Python Strings 

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• In Python, Strings are stored as individual characters in a contiguous memory location. 
  
• The benefit of using String is that it can be accessed from both the directions (forward and backward).
• Both forward as well as backward indexing are provided using Strings in Python.
• Forward indexing starts with 0,1,2,3,.... 
• Backward indexing starts with -1,-2,-3,-4,....

        str[0]='P'=str[-6] ,
        str[1]='Y' = str[-5] ,
        str[2] = 'T' = str[-4] ,
        str[3] = 'H' = str[-3] ,
        str[4] = 'O' = str[-2] , 
        str[5] = 'N' = str[-1]. 
        

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Python String Example

Here, we are creating a simple program to retrieve String in reverse as well as normal form.

        name="Rajat"  
        length=len(name)  
        i=0  
        
        for n in range(-1,(-length-1),-1):  
            print(name[i],"\t",name[n])  
            i+=1
        

output : 

        R         t
        
        a         a
        
        j         j
        
        a         a
        
        t         R
        

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Python Strings Operators

To perform operation on string, Python provides basically 3 types of Operators that are given below.

• Basic Operators.
• Membership Operators.
• Relational Operators.

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1. Basic Operators

There are two types of basic operators in String + and *.

String Concatenation Operator (+)

        str1="apk"
        str2="Zube"
        print(str1+str2)
        

Output :

        apkZube
        

String Concatenation Operator (+)

Expression	Output
"10"+"50"	"1050"
"apk"+"007"	"apk007"
"apk97"+"zube97"	"apk97zube97"

NOTE: Both the operands passed for concatenation must be of same type, else it will show an error.

for example :

        print("apkZube"+97)
        

output :

        Traceback (most recent call last):
          File "main.py", line 1, in 
            print("apkZube"+97)
        TypeError: Can't convert 'int' object to str implicitly 
        

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Python String Replication Operator (*)

Replication operator uses two parameters for operation, One is the integer value and the other one is the String argument.

The Replication operator is used to repeat a string number of times. The string will be repeated the number of times which is given by the integer value.

For Example :

        print("ApkZube" * 5)
        print(3 * "Python")
        

output : 

        ApkZubeApkZubeApkZubeApkZubeApkZube
        PythonPythonPython
        

Python String Replication Operator (*)

Expression	Output
"ArcX" * 2	"ArcXArcX"
3 * '5'	'555'
'@' * 5	'@@@@@'

NOTE: We can use Replication operator in any way i.e., int * string or string * int. Both the parameters passed cannot be of same type.

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2 . Python String Membership Operators

Membership Operators are already discussed in the Operators section. Let see with context of String.

There are two types of Membership operators :

1. in - "in" operator returns true if a character or the entire substring is present in the specified string, otherwise false.
2. not in - "not in" operator returns true if a character or entire substring does not exist in the specified string, otherwise false.

lets see the example :

        

str1="ApkZube"
str2="Apk"
str3="Zube"
str4="Dev"

print('Exmple of in operator ::')
print(str2 in str1)
print(str3 in str1)
print(str4 in str1)
print()
print(str2 not in str1)
print(str3 not in str1)
print(str4 not in str1)
        

output :

        

Exmple of in operator ::

True
True
False  


False
False
True  
        

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3. Python Relational Operators 

All the comparison (relational) operators i.e., (<,><=,>=,==,!=,<>) are also applicable for strings. The Strings are compared based on the ASCII value or Unicode(i.e., dictionary Order).

Example : 

        

print("ApkZube"=="ApkZube")
print("apkZube">="ApkZube")
print("A"<"a")
        

output :

        True
        True
        True
        

Explanation:

The ASCII value of a is 97, b is 98, c is 99 and so on. The ASCII value of A is 65, B is 66, C is 67 and so on. The comparison between strings are done on the basis on ASCII value.

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Python String Slice Notation

Python String slice can be defined as a substring which is the part of the string. Therefore further substring can be obtained from a string.

There can be many forms to slice a string, as string can be accessed or indexed from both the direction and hence string can also be sliced from both the directions.

Syntax of Slice Operator :

str[start : stop : step ]

other syntax of slice 

str[start : stop]  #items start through stop-1

str[start : ] #items start through the rest of the array

str[ : stop]  #items from the beginning through stop-1

str[ : ]  # a copy of the whole array

example :

        s="Monty Python"
        
        print(s[6:10])
        print(s[-12:-7])
        print(s[-1: :-1]) #reversed all string
        print(s[2: 10: 2]) #step = 2
        print(s[ : : -1]) #reversed all string
        print(s[ : 5]) #from 0 to 4
        print(s[3 : ]) #from 3 to end of the string
        print(s[ : ]) #copy all strin
        
        

output :

        Pyth
        Monty
        nohtyP ytnoM
        nyPt
        nohtyP ytnoM
        Monty
        ty Python
        Monty Python
        

NOTE: Both the operands passed for concatenation must be of same type, else it will show an error.

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