Merge pull request RustPython#4272 from oow214/iter_combi_reduce

Add `combinations.__reduce__ `

Author: youknowone

vm/src/stdlib/itertools.rs

@@ -3,7 +3,10 @@ pub(crate) use decl::make_module;
 #[pymodule(name = "itertools")]
 mod decl {
     use crate::{
-        builtins::{int, PyGenericAlias, PyInt, PyIntRef, PyList, PyTuple, PyTupleRef, PyTypeRef},
+        builtins::{
+            int, tuple::IntoPyTuple, PyGenericAlias, PyInt, PyIntRef, PyList, PyTuple, PyTupleRef,
+            PyTypeRef,
+        },
         common::{
             lock::{PyMutex, PyRwLock, PyRwLockWriteGuard},
             rc::PyRc,
@@ -1308,6 +1311,7 @@ mod decl {
     struct PyItertoolsCombinations {
         pool: Vec<PyObjectRef>,
         indices: PyRwLock<Vec<usize>>,
+        result: PyRwLock<Option<Vec<PyObjectRef>>>,
         r: AtomicCell<usize>,
         exhausted: AtomicCell<bool>,
     }
@@ -1341,6 +1345,7 @@ mod decl {
             PyItertoolsCombinations {
                 pool,
                 indices: PyRwLock::new((0..r).collect()),
+                result: PyRwLock::new(None),
                 r: AtomicCell::new(r),
                 exhausted: AtomicCell::new(r > n),
             }
@@ -1350,7 +1355,36 @@ mod decl {
     }
 
     #[pyclass(with(IterNext, Constructor))]
-    impl PyItertoolsCombinations {}
+    impl PyItertoolsCombinations {
+        #[pymethod(magic)]
+        fn reduce(zelf: PyRef<Self>, vm: &VirtualMachine) -> PyTupleRef {
+            let r = zelf.r.load();
+
+            let class = zelf.class().to_owned();
+
+            if zelf.exhausted.load() {
+                return vm.new_tuple((
+                    class,
+                    vm.new_tuple((vm.ctx.empty_tuple.clone(), vm.ctx.new_int(r))),
+                ));
+            }
+
+            let tup = vm.new_tuple((zelf.pool.clone().into_pytuple(vm), vm.ctx.new_int(r)));
+
+            if zelf.result.read().is_none() {
+                vm.new_tuple((class, tup))
+            } else {
+                let mut indices: Vec<PyObjectRef> = Vec::new();
+
+                for item in &zelf.indices.read()[..r] {
+                    indices.push(vm.new_pyobj(*item));
+                }
+
+                vm.new_tuple((class, tup, indices.into_pytuple(vm)))
+            }
+        }
+    }
+
     impl IterNextIterable for PyItertoolsCombinations {}
     impl IterNext for PyItertoolsCombinations {
         fn next(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
@@ -1367,38 +1401,48 @@ mod decl {
                 return Ok(PyIterReturn::Return(vm.new_tuple(()).into()));
             }
 
-            let res = vm.ctx.new_tuple(
-                zelf.indices
-                    .read()
-                    .iter()
-                    .map(|&i| zelf.pool[i].clone())
-                    .collect(),
-            );
+            let mut result_lock = zelf.result.write();
+            let result = if let Some(ref mut result) = *result_lock {
+                let mut indices = zelf.indices.write();
 
-            let mut indices = zelf.indices.write();
+                // Scan indices right-to-left until finding one that is not at its maximum (i + n - r).
+                let mut idx = r as isize - 1;
+                while idx >= 0 && indices[idx as usize] == idx as usize + n - r {
+                    idx -= 1;
+                }
 
-            // Scan indices right-to-left until finding one that is not at its maximum (i + n - r).
-            let mut idx = r as isize - 1;
-            while idx >= 0 && indices[idx as usize] == idx as usize + n - r {
-                idx -= 1;
-            }
+                // If no suitable index is found, then the indices are all at
+                // their maximum value and we're done.
+                if idx < 0 {
+                    zelf.exhausted.store(true);
+                    return Ok(PyIterReturn::StopIteration(None));
+                } else {
+                    // Increment the current index which we know is not at its
+                    // maximum.  Then move back to the right setting each index
+                    // to its lowest possible value (one higher than the index
+                    // to its left -- this maintains the sort order invariant).
+                    indices[idx as usize] += 1;
+                    for j in idx as usize + 1..r {
+                        indices[j] = indices[j - 1] + 1;
+                    }
 
-            // If no suitable index is found, then the indices are all at
-            // their maximum value and we're done.
-            if idx < 0 {
-                zelf.exhausted.store(true);
-            } else {
-                // Increment the current index which we know is not at its
-                // maximum.  Then move back to the right setting each index
-                // to its lowest possible value (one higher than the index
-                // to its left -- this maintains the sort order invariant).
-                indices[idx as usize] += 1;
-                for j in idx as usize + 1..r {
-                    indices[j] = indices[j - 1] + 1;
+                    // Update the result tuple for the new indices
+                    // starting with i, the leftmost index that changed
+                    for i in idx as usize..r {
+                        let index = indices[i];
+                        let elem = &zelf.pool[index];
+                        result[i] = elem.to_owned();
+                    }
+
+                    result.to_vec()
                 }
-            }
+            } else {
+                let res = zelf.pool[0..r].to_vec();
+                *result_lock = Some(res.clone());
+                res
+            };
 
-            Ok(PyIterReturn::Return(res.into()))
+            Ok(PyIterReturn::Return(vm.ctx.new_tuple(result).into()))
         }
     }