Python variable references

New to Python and picking up some practice on DSA problems though I have previously only worked in Java. Why does option 2 work and option 1 does not? I have seen Python passes by object reference and suspect the answer is to do with using references of references.

Option 1

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

class Solution:
    def middleNode(self, head: Optional[ListNode]) -> Optional[ListNode]:
        current = head
        fastp = current
        slowp = current

        while (current and current.next):
            fastp = fastp.next.next
            slowp = slowp.next
            current = current.next                 
        return slowp

Option 2

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

class Solution:
    def middleNode(self, head: Optional[ListNode]) -> Optional[ListNode]:
        fastp = head
        slowp = head

        while (fastp and fastp.next):
            fastp = fastp.next.next
            slowp = slowp.next                    
        return slowp

Shown 2 example solutions above, one working and one incorrect but unsure why.