Renamed octal_to_decimal to octal_to_decimal.py (TheAlgorithms#3420)

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

Author: cybov

Diff for: conversions/octal_to_decimal renamed to conversions/octal_to_decimal.py

@@ -9,10 +9,16 @@ def oct_to_decimal(oct_string: str) -> int:
     >>> 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("")
-    ValueError: Empty string value was passed to the function
+    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()
@@ -21,7 +27,7 @@ def oct_to_decimal(oct_string: str) -> int:
     is_negative = oct_string[0] == "-"
     if is_negative:
         oct_string = oct_string[1:]
-    if not all(0 <= int(char) <= 7 for char in oct_string):
+    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: