Renamed octal_to_decimal to octal_to_decimal.py (#3420)

* Renamed octal_to_decimal to octal_to_decimal.py
* Updated octal_to_decimal.py
* modified doctests
* updated octal_to_decimal.py

conversions/octal_to_decimal.py

@@ -0,0 +1,43 @@
+def oct_to_decimal(oct_string: str) -> int:
+    """
+    Convert a octal value to its decimal equivalent
+
+    >>> oct_to_decimal("12")
+    10
+    >>> oct_to_decimal(" 12   ")
+    10
+    >>> oct_to_decimal("-45")
+    -37
+    >>> oct_to_decimal("2-0Fm")
+    Traceback (most recent call last):
+    ...
+    ValueError: Non-octal value was passed to the function
+    >>> oct_to_decimal("")
+    Traceback (most recent call last):
+    ...
+    ValueError: Empty string was passed to the function
+    >>> oct_to_decimal("19")
+    Traceback (most recent call last):
+    ...
+    ValueError: Non-octal value was passed to the function
+    """
+    oct_string = str(oct_string).strip()
+    if not oct_string:
+        raise ValueError("Empty string was passed to the function")
+    is_negative = oct_string[0] == "-"
+    if is_negative:
+        oct_string = oct_string[1:]
+    if not oct_string.isdigit() or not all(0 <= int(char) <= 7 for char in oct_string):
+        raise ValueError("Non-octal value was passed to the function")
+    decimal_number = 0
+    for char in oct_string:
+        decimal_number = 8 * decimal_number + int(char)
+    if is_negative:
+        decimal_number = -decimal_number
+    return decimal_number
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()