LeetCode DSA Series #8: 1290. Convert Binary Number in a Linked List to Integer

This is my eighth submission to the challenge. The problem today is 1290. Convert Binary Number in a Linked List to Integer

Given head which is a reference node to a singly-linked list. The value of each node in the linked list is either 0 or 1. The linked list holds the binary representation of a number.
Return the decimal value of the number in the linked list.
The most significant bit is at the head of the linked list.

Here is my solution:

class Solution:
    def getDecimalValue(self, head: Optional[ListNode]) -> int:
        binary = ""
        while head.next:
            binary += str(head.val)
            head = head.next
        binary += str(head.val)

        decimal = 0
        size = len(binary)
        for i in range(0, size):
            decimal += int(binary[i]) * 2**(size - i - 1)     

        return decimal

Is there a better way to do this? Please let me know.