LeetCode #2: Add Two Numbers

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:

class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

    def __str__(self):
        if self.next:
            return f"{self.val}{self.next}"
        else:
            return f"{self.val}"

import os
import pytest

from supplemental import ListNode

# --- helper methods ---
def from_py(*digits):
    digits = list(digits)
    head_node = ListNode(digits.pop(0))
    n = head_node
    while digits:
            n.next = ListNode(digits.pop(0))
            n = n.next
    return head_node

def to_py(head):
    r = []
    while head:
        r.append(head.val)
        head = head.next
    return r


def test_transformer():
    """ Make sure that the test tooling works. """
    for test_value in [ [1], [1,2], [1,2,3] ]:
        head = from_py(*test_value)
        print(f"{test_value} ==> {head}")
        assert to_py(head) == test_value

# --- END helper methods ---

class BaseTestClass:
    def test_vector_from_spec_ok(self):
        a = from_py(2,4,3)
        b = from_py(5,6,4)

        assert to_py(self.addTwoNumbers(a, b)) == [7,0,8]

    def test_adding_zeros_ok(self):
        a = from_py(0)
        b = from_py(0)

        assert to_py(self.addTwoNumbers(a, b)) == [0]

    def test_adding_carry_ok(self):
        a = from_py(5)
        b = from_py(7)

        assert to_py(self.addTwoNumbers(a, b)) == [2,1]

    def test_different_lengths(self):
        a = from_py(1,8)
        b = from_py(0)

        assert to_py(self.addTwoNumbers(a, b)) == [1,8]

from supplemental import ListNode

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        carry = 0
        head = None
        tail = None
        while l1 or l2:
            v1 = l1.val if l1 else 0
            v2 = l2.val if l2 else 0

            sum = v1 + v2 + carry
            digit = sum % 10
            carry = 1 if sum >= 10 else 0

            if head is None:
                head = ListNode(digit)
                tail = head
            else:
                tail.next = ListNode(digit)
                tail = tail.next

            if l1: l1 = l1.next
            if l2: l2 = l2.next
        if carry:
            tail.next = ListNode(carry)
        return head

============================= test session starts ==============================
platform linux -- Python 3.7.5, pytest-3.10.1, py-1.8.0, pluggy-0.12.0
benchmark: 3.2.2 (defaults: timer=time.perf_counter disable_gc=False min_rounds=5 min_time=0.000005 max_time=1.0 calibration_precision=10 warmup=False warmup_iterations=100000)
rootdir: /home/jens/Documents/leetcode.com/002-add_two_numbers, inifile:
plugins: benchmark-3.2.2, profiling-1.7.0
collected 4 items

test_1a-solution.py ....                                                 [100%]

============================ slowest test durations ============================

(0.00 durations hidden.  Use -vv to show these durations.)
=========================== 4 passed in 0.03 seconds ===========================


Tests ran in 0.17746263899607584 seconds