From d32e5501be0d3407fed01f76c65f4c90b7c3604e Mon Sep 17 00:00:00 2001
From: Padraic Fanning <fanninpm@miamioh.edu>
Date: Thu, 25 Feb 2021 15:53:50 -0500
Subject: [PATCH] Add optional arguments to list.index()

More or less directly translated from the CPython implementation.
---
 vm/src/builtins/list.rs | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/vm/src/builtins/list.rs b/vm/src/builtins/list.rs
index c2314e5e2..a2ac44184 100644
--- a/vm/src/builtins/list.rs
+++ b/vm/src/builtins/list.rs
@@ -271,8 +271,35 @@ impl PyList {
     }
 
     #[pymethod]
-    fn index(&self, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
-        for (index, element) in self.borrow_value().clone().iter().enumerate() {
+    fn index(
+        &self,
+        needle: PyObjectRef,
+        start: OptionalArg<isize>,
+        stop: OptionalArg<isize>,
+        vm: &VirtualMachine,
+    ) -> PyResult<usize> {
+        let mut start = start.into_option().unwrap_or(0);
+        if start < 0 {
+            start += self.borrow_value().len() as isize;
+            if start < 0 {
+                start = 0;
+            }
+        }
+        let mut stop = stop.into_option().unwrap_or(isize::MAX);
+        if stop < 0 {
+            stop += self.borrow_value().len() as isize;
+            if stop < 0 {
+                stop = 0;
+            }
+        }
+        for (index, element) in self
+            .borrow_value()
+            .clone()
+            .iter()
+            .enumerate()
+            .take(stop as usize)
+            .skip(start as usize)
+        {
             if vm.identical_or_equal(element, &needle)? {
                 return Ok(index);
             }