How does Python's list.remove(value) determine what value to remove?
list, memory, python, python-internals
Solution
It iterates through the list, compares every item with the item to be removed and if it finds a match, it just removes that. It works in O(N). Source: https://wiki.python.org/moin/TimeComplexity
It removes only the first matched item and returns immediately.
If the item to be removed is not there, it fails with `ValueError`
This is the `listremove` function which removes the item from a list and it uses `PyObject_RichCompareBool` to check if the items are the same. And `PyObject_RichCompareBool` is implemented like this
/* Quick result when objects are the same.
Guarantees that identity implies equality. */
if (v == w) {
if (op == Py_EQ)
return 1;
else if (op == Py_NE)
return 0;
}
res = PyObject_RichCompare(v, w, op);
If the identity of the objects are the same (if both the objects are the same), then return `1` otherwise compare the values and return the result.
Problem
If I have list of objects: ``` l = [a, b, c] ``` Then I remove one of those objects: ``` l.remove(a) ``` How is python determining which item in the list to remove (under the hood)? Is it using the memory location of `a`? (which you can view with `hex(id(a))`)