Added decimal_to_binary_recursion.py (#3266)

* Added decimal_to_binary_recursion.py

* Added decimal_to_binary_recursion.py

* Made changes to docstring

* Use divmod()

* binary_recursive(div) + str(mod)

* Be kind with user input if possible

* Update decimal_to_binary_recursion.py

* ValueError: invalid literal for int() with base 10: 'number'

Co-authored-by: Christian Clauss <cclauss@me.com>

conversions/decimal_to_binary_recursion.py

@@ -0,0 +1,53 @@
+def binary_recursive(decimal: int) -> str:
+    """
+    Take a positive integer value and return its binary equivalent.
+    >>> binary_recursive(1000)
+    '1111101000'
+    >>> binary_recursive("72")
+    '1001000'
+    >>> binary_recursive("number")
+    Traceback (most recent call last):
+    ...
+    ValueError: invalid literal for int() with base 10: 'number'
+    """
+    decimal = int(decimal)
+    if decimal in (0, 1):  # Exit cases for the recursion
+        return str(decimal)
+    div, mod = divmod(decimal, 2)
+    return binary_recursive(div) + str(mod)
+
+
+def main(number: str) -> str:
+    """
+    Take an integer value and raise ValueError for wrong inputs,
+    call the function above and return the output with prefix "0b" & "-0b"
+    for positive and negative integers respectively.
+    >>> main(0)
+    '0b0'
+    >>> main(40)
+    '0b101000'
+    >>> main(-40)
+    '-0b101000'
+    >>> main(40.8)
+    Traceback (most recent call last):
+    ...
+    ValueError: Input value is not an integer
+    >>> main("forty")
+    Traceback (most recent call last):
+    ...
+    ValueError: Input value is not an integer
+    """
+    number = str(number).strip()
+    if not number:
+        raise ValueError("No input value was provided")
+    negative = "-" if number.startswith("-") else ""
+    number = number.lstrip("-")
+    if not number.isnumeric():
+        raise ValueError("Input value is not an integer")
+    return f"{negative}0b{binary_recursive(int(number))}"
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()