Python program to convert camel case string to snake case

Given a string in camel case, write a Python program to convert the given string from camel case to snake case.

Examples:

Input : GeeksForGeeks
Output : geeks_for_geeks

Input : ThisIsInCamelCase
Output : this_is_in_camel_case

Let’s see the different ways we can do this task.

Method #1 : Naive Approach

This is a naive implementation to convert camel case to snake case. First, we initialize a variable ‘res’ with an empty list and append first character (in lower case) to it. Now, Each time we encounter a Capital alphabet, we append ‘_’ and the alphabet (in lower case) to ‘res’, otherwise, just append the alphabet only.

# Python3 program to convert string  
# from camel case to snake case 
  
def change_case(str): 
    res = [str[0].lower()] 
    for c in str[1:]: 
        if c in ('ABCDEFGHIJKLMNOPQRSTUVWXYZ'): 
            res.append('_') 
            res.append(c.lower()) 
        else: 
            res.append(c) 
      
    return ''.join(res) 
      
# Driver code 
str = "GeeksForGeeks"
print(change_case(str)) 

Output:

geeks_for_geeks

Method #2 : List comprehension

# Python3 program to convert string  
# from camel case to snake case 
  
def change_case(str): 
      
    return ''.join(['_'+i.lower() if i.isupper()  
               else i for i in str]).lstrip('_') 
      
# Driver code 
str = "GeeksForGeeks"
print(change_case(str)) 

Output:

geeks_for_geeks

Method #3 : Python reduce()

Python reduce() method applies a function to all the string alphabets, that wherever it find uppercase alphabet, it add ‘_’ in front of it and replace the uppercase alphabet with lowercase alphabet.

# Python3 program to convert string  
# from camel case to snake case 
from functools import reduce
  
def change_case(str): 
      
    return reduce(lambda x, y: x + ('_' if y.isupper() else '') + y, str).lower() 
      
# Driver code 
str = "GeeksForGeeks"
print(change_case(str)) 

Output:

geeks_for_geeks

Method #4 : Python Regex

# Python3 program to convert string  
# from camel case to snake case 
import re 
  
def change_case(str): 
    s1 = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', str) 
    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', s1).lower() 
      
# Driver code 
str = "GeeksForGeeks"
print(change_case(str)) 

Output:

geeks_for_geeks

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