How to check if a string starts with a substring using regex in Python?

Last Updated : 29 Dec, 2020

Prerequisite: Regular Expression in Python

Given a string str, the task is to check if a string starts with a given substring or not using regular expression.

Examples:

Input: String: "geeks for geeks makes learning fun" 
       Substring: "geeks" 
Output: True 
Input: String: "geeks for geeks makes learning fun" 
       Substring: "makes" 
Output: False

Approach 1:
Here, we first check a given substring present in a string or not if yes then we use search() function of re library along with metacharacter “^”. This metacharacter checks for a given string starts with substring provided or not.

Below is the implementation of the above approach:

Python3

# import library 
import re 
  
# define a function  
def find(string, sample) : 
    
  # check substring present  
  # in a string or not 
  if (sample in string): 
  
      y = "^" + sample 
  
      # check if string starts  
      # with the substring 
      x = re.search(y, string) 
  
      if x : 
          print("string starts with the given substring") 
  
      else : 
          print("string doesn't start with the given substring") 
  
  else : 
      print("entered string isn't a substring") 
  
  
# Driver code 
string = "geeks for geeks makes learning fun"  
sample = "geeks"
  
# function call 
find(string, sample) 
  
sample = "makes"
  
# function call 
find(string, sample) 

Output:

string starts with the given substring
string doesn't start with the given substring

Approach 2:
Here, we first check a given substring present in a string or not if yes then we use search() function of re library along with metacharacter “\A”. This metacharacter checks for a given string starts with substring provided or not.

Below is the implementation of the above approach:

Python3

# import library 
import re 
  
# define a function  
def find(string, sample) : 
    
  # check substring present  
  # in a string or not 
  if (sample in string): 
  
      y = "\A" + sample 
  
      # check if string starts  
      # with the substring 
      x = re.search(y, string) 
  
      if x : 
          print("string starts with the given substring") 
  
      else : 
          print("string doesn't start with the given substring") 
  
  else : 
      print("entered string isn't a substring") 
  
  
# Driver code 
string = "geeks for geeks makes learning fun"  
sample = "geeks"
  
# function call 
find(string, sample) 
  
sample = "makes"
  
# function call 
find(string, sample) 

Output:

string starts with the given substring
string doesn't start with the given substring

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