From b4069afec306fa40a020ecd06c2256eaf22cbd72 Mon Sep 17 00:00:00 2001
From: Marek Mazij <112333347+Mrk-Mzj@users.noreply.github.com>
Date: Wed, 4 Oct 2023 19:43:08 +0200
Subject: [PATCH 1/2] First commit

camel case to snake case conversion algorithm, including numbers
---
 strings/camel_case_to_snake_case.py | 55 +++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 strings/camel_case_to_snake_case.py

diff --git a/strings/camel_case_to_snake_case.py b/strings/camel_case_to_snake_case.py
new file mode 100644
index 000000000000..38051fed389e
--- /dev/null
+++ b/strings/camel_case_to_snake_case.py
@@ -0,0 +1,55 @@
+def camel_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("SomeRandomString")
+    'some_random_string'
+
+    >>> 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'>
+
+    """
+
+    import re
+
+    # check for invalid input type
+    if not isinstance(input_str, str):
+        msg = f"Expected string as input, found {type(input_str)}"
+        raise ValueError(msg)
+
+    # Replace all characters that are not letters or numbers with the underscore
+    snake_str = re.sub(r"[^a-zA-Z0-9]", "_", input_str)
+
+    # Find where lowercase meets uppercase. Insert underscore between them
+    snake_str = re.sub(r"([a-z])([A-Z])", r"\1_\2", snake_str).lower()
+
+    # Find the sequence of digits at the beginning
+    snake_str = re.sub(r"^(\d+)", r"\1_", snake_str)
+
+    # Find the sequence of digits at the end
+    snake_str = re.sub(r"(\d+)$", r"_\1", snake_str)
+
+    # Find where letter meets digits
+    snake_str = re.sub(r"([a-z])(\d+)", r"\1_\2", snake_str)
+
+    # Find where digits meet letter
+    snake_str = re.sub(r"(\d+)([a-z])", r"\1_\2", snake_str)
+
+    return snake_str
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()

From 28f41df979d496f45e28102b537c44548bd46219 Mon Sep 17 00:00:00 2001
From: Marek Mazij <112333347+Mrk-Mzj@users.noreply.github.com>
Date: Thu, 5 Oct 2023 20:36:07 +0200
Subject: [PATCH 2/2] code modified to not use regex

---
 strings/camel_case_to_snake_case.py | 37 ++++++++++++++++-------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/strings/camel_case_to_snake_case.py b/strings/camel_case_to_snake_case.py
index 38051fed389e..582907be2edb 100644
--- a/strings/camel_case_to_snake_case.py
+++ b/strings/camel_case_to_snake_case.py
@@ -5,8 +5,8 @@ def camel_to_snake_case(input_str: str) -> str:
     >>> camel_to_snake_case("someRandomString")
     'some_random_string'
 
-    >>> 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'
@@ -21,30 +21,35 @@ def camel_to_snake_case(input_str: str) -> str:
 
     """
 
-    import re
-
     # check for invalid input type
     if not isinstance(input_str, str):
         msg = f"Expected string as input, found {type(input_str)}"
         raise ValueError(msg)
 
-    # Replace all characters that are not letters or numbers with the underscore
-    snake_str = re.sub(r"[^a-zA-Z0-9]", "_", input_str)
+    snake_str = ""
+
+    for index, char in enumerate(input_str):
+        if char.isupper():
+            snake_str += "_" + char.lower()
 
-    # Find where lowercase meets uppercase. Insert underscore between them
-    snake_str = re.sub(r"([a-z])([A-Z])", r"\1_\2", snake_str).lower()
+        # if char is lowercase but proceeded by a digit:
+        elif input_str[index - 1].isdigit() and char.islower():
+            snake_str += "_" + char
 
-    # Find the sequence of digits at the beginning
-    snake_str = re.sub(r"^(\d+)", r"\1_", snake_str)
+        # if char is a digit proceeded by a letter:
+        elif input_str[index - 1].isalpha() and char.isnumeric():
+            snake_str += "_" + char.lower()
 
-    # Find the sequence of digits at the end
-    snake_str = re.sub(r"(\d+)$", r"_\1", snake_str)
+        # if char is not alphanumeric:
+        elif not char.isalnum():
+            snake_str += "_"
 
-    # Find where letter meets digits
-    snake_str = re.sub(r"([a-z])(\d+)", r"\1_\2", snake_str)
+        else:
+            snake_str += char
 
-    # Find where digits meet letter
-    snake_str = re.sub(r"(\d+)([a-z])", r"\1_\2", snake_str)
+    # remove leading underscore
+    if snake_str[0] == "_":
+        snake_str = snake_str[1:]
 
     return snake_str