From e9c64168d9fb9c3d0ce94b537eb7cd9728abd379 Mon Sep 17 00:00:00 2001
From: hauntsaninja <>
Date: Tue, 22 Feb 2022 12:49:07 -0800
Subject: [PATCH] Import packaging.version in torch_version, if available
 (#71902)
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Summary:
Resolves https://github.com/pytorch/pytorch/issues/71280

We used to use `from pkg_resources import packaging`. To recap, this has
three potential problems:
1) `pkg_resources` is a really slow import
2) We have an undeclared runtime dependency on `setuptools`
3) We're relying on `pkg_resources`'s secret vendored copy of
   `packaging`. This is obviously not part of the public API of
   `pkg_resources`.

In https://github.com/pytorch/pytorch/issues/71345 this was made a lazy import, which is great! It means we don't
run into these problems as long as users don't use `torch.__version__`.

This change additionally helps further address problems 1 and 3, by
directly importing `packaging`, if present, and only falling back to the
vendored copy in `pkg_resources`.

Benchmark for speed difference in a virtual environment with a couple
hundred packages installed:
```
λ hyperfine -w 2 'python -c "from pkg_resources import packaging"' 'python -c "import packaging.version"'
Benchmark 1: python -c "from pkg_resources import packaging"
  Time (mean ± σ):     706.7 ms ±  77.1 ms    [User: 266.5 ms, System: 156.8 ms]
  Range (min … max):   627.9 ms … 853.2 ms    10 runs

Benchmark 2: python -c "import packaging.version"
  Time (mean ± σ):      53.8 ms ±   8.5 ms    [User: 34.8 ms, System: 14.4 ms]
  Range (min … max):    46.3 ms …  72.3 ms    53 runs
  'python -c "import packaging.version"' ran
   13.14 ± 2.52 times faster than 'python -c "from pkg_resources import packaging"'
```

Pull Request resolved: https://github.com/pytorch/pytorch/pull/71902

Reviewed By: mikaylagawarecki

Differential Revision: D34343145

Pulled By: malfet

fbshipit-source-id: a6bd7ecf0cbb6b5c20ab18a22576aa2df9eb3324
(cherry picked from commit 0a249044c8f83ecbc81b6d1e7a16541b82b74243)
---
 torch/torch_version.py | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/torch/torch_version.py b/torch/torch_version.py
index a7aa6764b5d..9fd989a44ff 100644
--- a/torch/torch_version.py
+++ b/torch/torch_version.py
@@ -8,7 +8,7 @@ class _LazyImport:
        def v():
            return Version('1.2.3')
     and
-       Versoin = _LazyImport('Version')
+       Version = _LazyImport('Version')
        def v():
            return Version('1.2.3')
     The difference here is that in later example imports
@@ -18,7 +18,12 @@ class _LazyImport:
         self._cls_name = cls_name
 
     def get_cls(self):
-        from pkg_resources import packaging  # type: ignore[attr-defined]
+        try:
+            import packaging.version  # type: ignore[import]
+        except ImportError:
+            # If packaging isn't installed, try and use the vendored copy
+            # in pkg_resources
+            from pkg_resources import packaging  # type: ignore[attr-defined]
         return getattr(packaging.version, self._cls_name)
 
     def __call__(self, *args, **kwargs):