bpo-33944: note about the intended use of code in .pth files (GH-10131)
https://bugs.python.org/issue33944
diff --git a/Doc/library/site.rst b/Doc/library/site.rst
index 9e4d402..e1ca160 100644
--- a/Doc/library/site.rst
+++ b/Doc/library/site.rst
@@ -61,6 +61,19 @@
once. Blank lines and lines beginning with ``#`` are skipped. Lines starting
with ``import`` (followed by space or tab) are executed.
+.. note::
+
+ An executable line in a :file:`.pth` file is run at every Python startup,
+ regardless of whether a particular module is actually going to be used.
+ Its impact should thus be kept to a minimum.
+ The primary intended purpose of executable lines is to make the
+ corresponding module(s) importable
+ (load 3rd-party import hooks, adjust :envvar:`PATH` etc).
+ Any other initialization is supposed to be done upon a module's
+ actual import, if and when it happens.
+ Limiting a code chunk to a single line is a deliberate measure
+ to discourage putting anything more complex here.
+
.. index::
single: package
triple: path; configuration; file
diff --git a/Misc/NEWS.d/next/Documentation/2018-10-26-18-10-29.bpo-33944.V1YeOA.rst b/Misc/NEWS.d/next/Documentation/2018-10-26-18-10-29.bpo-33944.V1YeOA.rst
new file mode 100644
index 0000000..29bec88
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2018-10-26-18-10-29.bpo-33944.V1YeOA.rst
@@ -0,0 +1 @@
+Added a note about the intended use of code in .pth files.