Issue #18416: Have importlib.machinery.PathFinder treat '' as the cwd

and stop importlib.machinery.FileFinder treating '' as '.'.

Previous PathFinder transformed '' into '.' which led to __file__ for
modules imported from the cwd to always be relative paths. This meant
the values of the attribute were wrong as soon as the cwd changed.
This change now means that as long as the site module is run (which
makes all entries in sys.path absolute) then all values for __file__
will also be absolute unless it's for __main__ when specified by file
path in a relative way (modules imported by runpy will have an
absolute path).

Now that PathFinder is no longer treating '' as '.' it only makes
sense for FileFinder to stop doing so as well. Now no transformation
is performed for the directory given to the __init__ method.

Thanks to Madison May for the initial patch.

1 files changed, 7 insertions, 0 deletions

diff --git a/Misc/NEWS b/Misc/NEWS
index 26dcb22..cc7906d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,13 @@ Projected release date: 2013-10-20
 Core and Builtins
 -----------------
 
+- Issue #18416: importlib.machinery.PathFinder now treats '' as the cwd and
+  importlib.machinery.FileFinder no longer special-cases '' to '.'. This leads
+  to modules imported from cwd to now possess an absolute file path for
+  __file__ (this does not affect modules specified by path on the CLI but it
+  does affect -m/runpy). It also allows FileFinder to be more consistent by not
+  having an edge case.
+
 - Issue #4555: All exported C symbols are now prefixed with either
   "Py" or "_Py".