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Python | Check if given string is numeric or not

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  • Last Updated : 09 Nov, 2022
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Given a string, write a Python program to check if the string is numeric or not. 

Examples: 

Input:  28
Output: digit

Input: a
Output: not a digit. 

Input: 21ab
Output: not a digit. 

Code #1: Using Python regex 

re.search(): This method either returns None (if the pattern doesn’t match) or a re.MatchObject contains information about the matching part of the string. This method stops after the first match, so this is best suited for testing a regular expression more than extracting data.  

Python3




# Python program to identify the Digit
 
# import re module
 
# re module provides support
# for regular expressions
import re
 
# Make a regular expression
# for identifying a digit
regex = '^[0-9]+$'
     
# Define a function for
# identifying a Digit
def check(string):
 
     # pass the regular expression
     # and the string in search() method
    if(re.search(regex, string)):
        print("Digit")
         
    else:
        print("Not a Digit")
     
 
# Driver Code
if __name__ == '__main__' :
     
    # Enter the string
    string = "28"
     
    # calling run function
    check(string)
 
    string = "a"
    check(string)
 
    string = "21ab"
    check(string)
 
    string = "12ab12"
    check(string)

Output: 

Digit
Not a Digit
Not a Digit
Not a Digit

 

  
Code #2: Using string.isnumeric() function

Python3




# Python code to check if string is numeric or not
     
# checking for numeric characters
string = '123ayu456'
print(string.isnumeric())
    
string = '123456'
print(string.isnumeric())

Output: 

False
True

 

Code #3: Without any built-in methods

Python3




# Python code to check if string is numeric or not
     
# checking for numeric characters
numerics="0123456789"
string = "123456"
c=0
for i in string:
    if i in numerics:
        c+=1
res=False
if(c==len(string)):
    res=True
print(res)

Output

True

Code #4 : Using replace() and len() methods

Python3




# Python code to check if string is numeric or not
     
# checking for numeric characters
numerics="0123456789"
string = "123456"
for i in numerics:
    string=string.replace(i,"")
res=False
if(len(string)==0):
    res=True
print(res)

Output

True

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