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Python Strings and its implementation



Learn: What is the String in Python, string’s declarations, define and its implementation in Python with Examples and Explanations?
Submitted by Shubham Singh Rajawat, on August 05, 2017

Strings in python are immutable means they cannot be changed once defined.

Example 1: #program to show that strings are immutable

string ="include"
string[5]="i"

Output

Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    string[5]="i"
TypeError: 'str' object does not support item assignment

This proves that python for badges to change a pre defined string but we can do one thing we can reassign its value.

Example 2: #program to show that a string can be appended /reassigned

string="include"
print (string)
string+="help"
print (string)

Output

include
includehelp

So we append a string by reassigning its value.

Strings in python are most likely to be same as strings in other languages and are accessible in the same way also. We can define a string in two ways by using single quotes or double quotes.

Example 3: #program to define a string

string1="includehelp"
print (string1)
string2='includehelp'
print(string2)

Output

includehelp
includehelp

See outputs for both the strings are equal because they are considered same by python interpreter.

Indexing of strings in python starts with zero to length-1 i.e. if we want to access the first element of string we will use string[0]. Indexing also available from reverse side i.e. to access the last element we can also use string[-1] and string[-2] for second last element.

Example 4: #program to access a string

string="include help"
print(string[5])
print("include help"[5])
print(string[-1])
print(string[12])

Output

d
d
p
Traceback (most recent call last):
  File "<pyshell#8>>, line 1, in <module>
    print(string[12])
IndexError: string index out of range

strings can also be accessed like we accessed in line 3 of the above program but you should avoid using strings like this as every time you want to access any element of the string you have to write whole strings it would be much more difficult to do that, in line 4 error occurs because python checks for index out of bound condition.

We can also use triple quotes as a string but if a bare is used just after ‘def fun() ’ (any function) or at the starting of any module it will considered as ‘doc string ’ which contains the documentation of its object.

String slicing

String slicing means accessing a substring from the given string, this can be done by using a simple syntax.

string_name[beg:end:step]

Here,
beg : is the beginning index
end : is the end index but end is not inclusive
step : distance between every word (steps are optional)

If step is given -1 means a reverse string is returned.

Example 5: #program to implement string slicing

string="includehelp is a portal to learn concepts"
print(string[3:7])
print(string[:7])
print(string[15:])
print(string[0::3])
print(string[7:3:-1])
print(string[::-1])

Output

lude
include
a portal to learn concepts
ileliaoatlrcct
hedu
stpecnoc nrael ot latrop a si plehedulcni