camel_case_to_snake_case.py

defcamel_to_snake_case(input_str: str) ->str:
"""
 Transforms a camelCase (or PascalCase) string to snake_case

 >>> camel_to_snake_case("someRandomString")
 'some_random_string'

 >>> camel_to_snake_case("SomeRandomStr#ng")
 'some_random_str_ng'

 >>> camel_to_snake_case("123someRandom123String123")
 '123_some_random_123_string_123'

 >>> camel_to_snake_case("123SomeRandom123String123")
 '123_some_random_123_string_123'

 >>> camel_to_snake_case(123)
 Traceback (most recent call last):
 ...
 ValueError: Expected string as input, found <class 'int'>

 """

# check for invalid input type
ifnotisinstance(input_str, str):
msg=f"Expected string as input, found {type(input_str)}"
raiseValueError(msg)

snake_str=""

forindex, charinenumerate(input_str):
ifchar.isupper():
snake_str+="_"+char.lower()

# if char is lowercase but proceeded by a digit:
elifinput_str[index-1].isdigit() andchar.islower():
snake_str+="_"+char

# if char is a digit proceeded by a letter:
elifinput_str[index-1].isalpha() andchar.isnumeric():
snake_str+="_"+char.lower()

# if char is not alphanumeric:
elifnotchar.isalnum():
snake_str+="_"

else:
snake_str+=char

# remove leading underscore
ifsnake_str[0] =="_":
snake_str=snake_str[1:]

returnsnake_str


if__name__=="__main__":
fromdoctestimporttestmod

testmod()