Added type hints to ImageSequence

[radarhere]

Helps #2625

[hugovk]

Thanks!

---

Shall we add this and from typing import Self to Image.py so mypy --strict src/PIL/ImageSequence.py passes?

diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 1cb484b852..b121774095 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -1181,7 +1181,7 @@ class Image:
 
         return im
 
-    def copy(self):
+    def copy(self) -> Self:
         """
         Copies this image. Use this method if you wish to paste things
         into an image, but still retain the original.
@@ -2450,7 +2450,7 @@ class Image:
         if open_fp:
             fp.close()
 
-    def seek(self, frame):
+    def seek(self, frame: int) -> None:
         """
         Seeks to the given frame in this sequence file. If you seek
         beyond the end of the sequence, the method raises an
@@ -2537,7 +2537,7 @@ class Image:
 
         return self._new(self.im.getband(channel))
 
-    def tell(self):
+    def tell(self) -> int:
         """
         Returns the current frame number. See :py:meth:`~PIL.Image.Image.seek`.
 

---

Wondering if we should have a TypeAlias for Image.Image in Image.py?

Something like this?

from typing import TypeAlias

ImageType: TypeAlias = Image.Image

Or maybe explicit is better?

Anyway, not necessary for this PR.

[radarhere]

Testing, I find that from typing import Self is only available in Python >= 3.11. Apart from that though, I've made changes to allow --strict to pass.

[radarhere]

Wondering if we should have a TypeAlias for Image.Image in Image.py?

It turns out that TypeAlias was only added in Python 3.10 - https://docs.python.org/3/library/typing.html#typing.TypeAlias

[hugovk]

We should be able do it instead like ImageType = Image.Image:

For backwards compatibility, type aliases can also be created through simple assignment

https://docs.python.org/3/library/typing.html#type-aliases

[radarhere]

Ok, see what you think of #7639

[radarhere]

Further thought decided against the idea of #7639 / a type alias for Image.Image.