How to Sum the Strings in Python

The challenge

Create a function that takes 2 nonnegative integers in form of a string as an input, and outputs the sum (also as a string):

Example: (Input1, Input2 –>Output)

"4",  "5" --> "9"
"34", "5" --> "39"

Notes:

• If either input is an empty string, consider it as zero.
• Inputs and the expected output will never exceed the signed 32-bit integer limit (2^31 - 1)

The solution in Python code

Option 1:

def sum_str(a, b):
    return str(int(a or 0) + int(b or 0))

Option 2:

def sum_str(*values):
    return str(sum(int(s or '0') for s in values))

Option 3:

def sum_str(*args):
    return str(sum(map(lambda x: int(x) if x else 0, args)))

Test cases to validate our solution

import test
from solution import sum_str

@test.describe("Fixed Tests")
def basic_tests():
    
    @test.it("Sample Tests")
    def sample_tests():
        test.assert_equals(sum_str("4","5"), "9")
        test.assert_equals(sum_str("34","5"), "39")

    @test.it("Tests with empty strings")
    def empty_string():
        test.assert_equals(sum_str("9",""), "9", "x + empty = x")
        test.assert_equals(sum_str("","9"), "9", "empty + x = x")
        test.assert_equals(sum_str("","") , "0", "empty + empty = 0")