Refactor string.splitlines

vm/src/obj/objstr.rs

@@ -782,19 +782,25 @@ impl PyString {
         !self.value.is_empty() && self.value.chars().all(|c| c.is_ascii())
     }
 
-    // doesn't implement keep new line delimiter just yet
     #[pymethod]
     fn splitlines(&self, args: SplitLineArgs, vm: &VirtualMachine) -> PyObjectRef {
-        let end = if let OptionalArg::Present(true) = args.keepends {
-            "\n"
-        } else {
-            ""
-        };
-        let elements = self
-            .value
-            .split('\n')
-            .map(|e| vm.ctx.new_str(e.to_string() + end))
-            .collect();
+        let keepends = args.keepends.unwrap_or(false);
+        let mut elements = vec![];
+        let mut curr = "".to_string();
+        for ch in self.value.chars() {
+            if ch == '\n' {
+                if keepends {
+                    curr.push(ch);
+                }
+                elements.push(vm.ctx.new_str(curr.clone()));
+                curr.clear();
+            } else {
+                curr.push(ch);
+            }
+        }
+        if !curr.is_empty() {
+            elements.push(vm.ctx.new_str(curr.clone()));
+        }
         vm.ctx.new_list(elements)
     }