From 3d143e0dbb6b8a5486437ff034aadbb18907c58b Mon Sep 17 00:00:00 2001
From: Ohad Ravid <ohad.rv@gmail.com>
Date: Sun, 27 Jun 2021 09:45:15 +0300
Subject: [PATCH] Added `size_hint` impls for
 `{PyDict,PyList,PySet,PyTuple}Iterator`s

---
 CHANGELOG.md       | 1 +
 src/types/dict.rs  | 6 ++++++
 src/types/list.rs  | 6 ++++++
 src/types/set.rs   | 6 ++++++
 src/types/tuple.rs | 5 +++++
 5 files changed, 24 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 99a3e73b8e2..3994530c378 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Add `serde` feature which provides implementations of `Serialize` and `Deserialize` for `Py<T>`. [#1366](https://github.com/PyO3/pyo3/pull/1366)
 - Add FFI definition `_PyCFunctionFastWithKeywords` on Python 3.7 and up. [#1384](https://github.com/PyO3/pyo3/pull/1384)
 - Add `PyDateTime::new_with_fold()` method. [#1398](https://github.com/PyO3/pyo3/pull/1398)
+- Add `size_hint` impls for `{PyDict,PyList,PySet,PyTuple}Iterator`s. [#1699](https://github.com/PyO3/pyo3/pull/1699)
 
 ### Changed
 - `prepare_freethreaded_python` will no longer register an `atexit` handler to call `Py_Finalize`. This resolves a number of issues with incompatible C extensions causing crashes at finalization. [#1355](https://github.com/PyO3/pyo3/pull/1355)
diff --git a/src/types/dict.rs b/src/types/dict.rs
index abd0395894b..bc2b10bdf32 100644
--- a/src/types/dict.rs
+++ b/src/types/dict.rs
@@ -203,6 +203,12 @@ impl<'py> Iterator for PyDictIterator<'py> {
             }
         }
     }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.dict.len().unwrap_or_default();
+        (len, Some(len))
+    }
 }
 
 impl<'a> std::iter::IntoIterator for &'a PyDict {
diff --git a/src/types/list.rs b/src/types/list.rs
index 4a0586e4fcd..eca886ad377 100644
--- a/src/types/list.rs
+++ b/src/types/list.rs
@@ -151,6 +151,12 @@ impl<'a> Iterator for PyListIterator<'a> {
             None
         }
     }
+    
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.list.len();
+        (len, Some(len))
+    }
 }
 
 impl<'a> std::iter::IntoIterator for &'a PyList {
diff --git a/src/types/set.rs b/src/types/set.rs
index 3989edfb59e..7c2ea91be39 100644
--- a/src/types/set.rs
+++ b/src/types/set.rs
@@ -172,6 +172,12 @@ impl<'py> Iterator for PySetIterator<'py> {
             }
         }
     }
+    
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.set.len().unwrap_or_default();
+        (len, Some(len))
+    }
 }
 
 impl<'a> std::iter::IntoIterator for &'a PySet {
diff --git a/src/types/tuple.rs b/src/types/tuple.rs
index 9dbe9395164..7e8859b0f6c 100644
--- a/src/types/tuple.rs
+++ b/src/types/tuple.rs
@@ -121,6 +121,11 @@ impl<'a> Iterator for PyTupleIterator<'a> {
             None
         }
     }
+    
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.length, Some(self.length))
+    }
 }
 
 impl<'a> IntoIterator for &'a PyTuple {