Don't import pkg_resources unless we need to parse dev version numbers.

anntzer · anntzer · commit a62d442d2732 · 2021-03-07T23:49:53.000+01:00
pkg_resources can be very slow to import, although this depends on the
details of the python setup.  On my machine, this PR speeds up `import
sklearn` (with no dev versions of anything other than sklearn installed)
by ~33%, from ~550ms to ~360ms.
diff --git a/sklearn/utils/fixes.py b/sklearn/utils/fixes.py
@@ -24,11 +24,18 @@
 
 from .deprecation import deprecated
 
-try:
-    from pkg_resources import parse_version  # type: ignore
-except ImportError:
-    # setuptools not installed
-    parse_version = LooseVersion  # type: ignore
+
+def parse_version(v):
+    if not set(v) <= set("0123456789."):
+        # Avoid importing pkg_resources (which is slow) unless we need to parse
+        # dev version numbers.
+        try:
+            import pkg_resources
+        except ImportError:  # setuptools not installed.
+            pass
+        else:
+            return pkg_resources.parse_version(v)
+    return LooseVersion(v)
 
 
 np_version = parse_version(np.__version__)
