Merge pull request #1372 from j30ng/itertools-accumulate

Implement itertools.accumulate

tests/snippets/stdlib_itertools.py

@@ -209,4 +209,29 @@ assert 6 == next(it)
 assert 4 == next(it)
 assert 1 == next(it)
 with assertRaises(StopIteration):
-    next(it)
+    next(it)
+
+
+# itertools.accumulate
+it = itertools.accumulate([6, 3, 7, 1, 0, 9, 8, 8])
+assert 6 == next(it)
+assert 9 == next(it)
+assert 16 == next(it)
+assert 17 == next(it)
+assert 17 == next(it)
+assert 26 == next(it)
+assert 34 == next(it)
+assert 42 == next(it)
+with assertRaises(StopIteration):
+    next(it)
+
+it = itertools.accumulate([3, 2, 4, 1, 0, 5, 8], lambda a, v: a*v)
+assert 3 == next(it)
+assert 6 == next(it)
+assert 24 == next(it)
+assert 24 == next(it)
+assert 0 == next(it)
+assert 0 == next(it)
+assert 0 == next(it)
+with assertRaises(StopIteration):
+    next(it)

vm/src/stdlib/itertools.rs

@@ -537,6 +537,66 @@ impl PyItertoolsFilterFalse {
     }
 }
 
+#[pyclass]
+#[derive(Debug)]
+struct PyItertoolsAccumulate {
+    iterable: PyObjectRef,
+    binop: PyObjectRef,
+    acc_value: RefCell<Option<PyObjectRef>>,
+}
+
+impl PyValue for PyItertoolsAccumulate {
+    fn class(vm: &VirtualMachine) -> PyClassRef {
+        vm.class("itertools", "accumulate")
+    }
+}
+
+#[pyimpl]
+impl PyItertoolsAccumulate {
+    #[pymethod(name = "__new__")]
+    #[allow(clippy::new_ret_no_self)]
+    fn new(
+        cls: PyClassRef,
+        iterable: PyObjectRef,
+        binop: OptionalArg<PyObjectRef>,
+        vm: &VirtualMachine,
+    ) -> PyResult<PyRef<PyItertoolsAccumulate>> {
+        let iter = get_iter(vm, &iterable)?;
+
+        PyItertoolsAccumulate {
+            iterable: iter,
+            binop: binop.unwrap_or_else(|| vm.get_none()),
+            acc_value: RefCell::from(Option::None),
+        }
+        .into_ref_with_type(vm, cls)
+    }
+
+    #[pymethod(name = "__next__")]
+    fn next(&self, vm: &VirtualMachine) -> PyResult {
+        let iterable = &self.iterable;
+        let obj = call_next(vm, iterable)?;
+
+        let next_acc_value = match &*self.acc_value.borrow() {
+            Option::None => obj.clone(),
+            Option::Some(value) => {
+                if self.binop.is(&vm.get_none()) {
+                    vm._add(value.clone(), obj.clone())?
+                } else {
+                    vm.invoke(&self.binop, vec![value.clone(), obj.clone()])?
+                }
+            }
+        };
+        self.acc_value.replace(Option::from(next_acc_value.clone()));
+
+        Ok(next_acc_value)
+    }
+
+    #[pymethod(name = "__iter__")]
+    fn iter(zelf: PyRef<Self>, _vm: &VirtualMachine) -> PyRef<Self> {
+        zelf
+    }
+}
+
 pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
     let ctx = &vm.ctx;
 
@@ -561,6 +621,9 @@ pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
     let filterfalse = ctx.new_class("filterfalse", ctx.object());
     PyItertoolsFilterFalse::extend_class(ctx, &filterfalse);
 
+    let accumulate = ctx.new_class("accumulate", ctx.object());
+    PyItertoolsAccumulate::extend_class(ctx, &accumulate);
+
     py_module!(vm, "itertools", {
         "chain" => chain,
         "count" => count,
@@ -570,5 +633,6 @@ pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
         "takewhile" => takewhile,
         "islice" => islice,
         "filterfalse" => filterfalse,
+        "accumulate" => accumulate,
     })
 }