Python/conversions/decimal_to_binary_recursion.py

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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()