Skip to content
Related Articles
Open in App
Not now

Related Articles

Python | Get the numeric prefix of given string

Improve Article
Save Article
  • Last Updated : 04 Feb, 2023
Improve Article
Save Article

Given a string. the task is to print numeric prefix in string (if it is present in string). Given below are few methods to solve the task.

Method #1: Using Naive Method 

Python3




# Python code to demonstrate
# to get numeric prefix in string
# if present
 
# initialising string
ini_string = "123abcjw"
ini_string2 = "abceddfgh"
 
# printing string and its length
print ("initial string : ", ini_string, ini_string2)
 
# code to find numeric prefix in string
res1 = ''.join(c for c in ini_string if c in '0123456789')
res2 = ''.join(c for c in ini_string2 if c in '0123456789')
 
 
# printing resultant string
print ("first string result: ", str(res1))
print ("second string result: ", str(res2))

Output:

initial string :  123abcjw abceddfgh
first string result:  123
second string result:

Time Complexity: O(n + m), where n + m are the length of given strings
Auxiliary Space: O(n + m)

Method #2: Using takewhile 

Python3




# Python code to demonstrate
# to get numeric prefix in string
# if present
from itertools import takewhile
 
# initialising string
ini_string = "123abcjw"
ini_string2 = "abceddfgh"
 
# printing string and its length
print ("initial string : ", ini_string, ini_string2)
 
# code to find numeric prefix in string
res1 = ''.join(takewhile(str.isdigit, ini_string))
res2 = ''.join(takewhile(str.isdigit, ini_string2))
 
# printing resultant string
print ("first string result: ", res1)
print ("second string result: ", res2)

Output:

initial string :  123abcjw abceddfgh
first string result:  123
second string result:

Time complexity: O(n), where n is the length of the string, since the code uses a for loop to iterate through the string and calls the built-in method str.isdigit() for each character in the string.
Auxiliary space: O(m), where m is the length of the numeric prefix in the string. 

Method #3: Using re.sub 

Python3




# Python code to demonstrate
# to get numeric prefix in string
# if present
import re
 
# initialising string
ini_string = "123abcjw"
ini_string2 = "abceddfgh"
 
# printing string and its length
print ("initial string : ", ini_string, ini_string2)
 
# code to find numeric prefix in string
res1 = re.sub('\D.*', '', ini_string)
res2 = re.sub('\D.*', '', ini_string2)
 
 
# printing resultant string
print ("first string result: ", str(res1))
print ("second string result: ", str(res2))

Output:

initial string :  123abcjw abceddfgh
first string result:  123
second string result:

Time Complexity: O(n), where n is the length of the string.
Auxiliary Space: O(1).

Using Method #4: Using re.findall 

Python3




# Python code to demonstrate
# to get numeric prefix in string
# if present
import re
 
# initialising string
ini_string = "123abcjw"
ini_string2 = "abceddfgh"
 
# printing string and its length
print ("initial string : ", ini_string, ini_string2)
 
# code to find numeric prefix in string
res1 = ''.join(re.findall('\d+', ini_string))
res2 = ''.join(re.findall('\d+', ini_string2))
 
# printing resultant string
print ("first string result: ", str(res1))
print ("second string result: ", str(res2))

Output:

initial string :  123abcjw abceddfgh
first string result:  123
second string result:

Method #5: Using isalpha() method

Python3




# Python code to demonstrate
# to get numeric prefix in string
# if present
def fun(s):
    x=""
    for i in s:
        if i.isalpha():
            break
        else:
            x+=i
    return x
# initialising string
ini_string = "123abcjw"
ini_string2 = "abceddfgh"
 
# printing string and its length
print ("initial string : ", ini_string, ini_string2)
# code to find numeric prefix in string
res1 = fun(ini_string)
res2 = fun(ini_string2)
# printing resultant string
print ("first string result: ", res1)
print ("second string result: ", res2)

Output

initial string :  123abcjw abceddfgh
first string result:  123
second string result:  

Time Complexity : O(N)
Auxiliary Space : O(N)

Method #6: Using re.search()

In the above code, we are using the search function from the re module to find the longest prefix of numeric characters in the input string. The regular expression r’^\d+’ matches one or more digits at the beginning of the string (the ^ symbol represents the start of the string).

If a match is found, the search function returns a Match object representing the match. We can use the group method of this object to extract the matched string. If no match is found, search returns None, and we return an empty string instead.

Finally, we use the print function to output the resulting prefix for each example input string.

Python




import re
 
def get_numeric_prefix(s):
    """
    Extracts the numeric prefix from a string.
    """
    # Use a regular expression to match the longest prefix of numeric characters
    match = re.search(r'^\d+', s)
    if match:
        # Return the matched prefix
        return match.group()
    else:
        # If no match was found, return an empty string
        return ""
 
# Example usage
print(get_numeric_prefix("123abcjw"))
print(get_numeric_prefix("abceddfgh"))
print(get_numeric_prefix("123abcjw12"))
#This code is contributed by Edula Vinay Kumar Reddy

Output

123

123

Time Complexity O(n), where n is the length of the input string.
Auxiliary Space: O(n).


My Personal Notes arrow_drop_up
Related Articles

Start Your Coding Journey Now!