Ezio Melotti added the comment: Another thing that should be clarified, is the difference between __main__.py inside a package, and __main__.py inside a zip file. For packages, as far as I understand, __main__.py should be inside the package (i.e. pkg/__main__.py, in the same dir of pkg/__init__.py). This allows the package to be "executed" by doing "python3 -m pkg". For zip files, the __main__.py should be right inside the zip (i.e. file.zip/__main__.py). This allows the zip file to be "executed" by doing "python3 file.zip" (note that no -m is used here, and that "python3 -m file.zip" fails). While zipping a package that already contains a __main__.py, the right way to do it seems to be the following: 1) add the package to a zip file (i.e. file.zip/pkg/) 2) add another __main__.py to the zip (i.e. file.zip/__main__.py) 3) add 'import pkg.__main__' to file.zip/__main__.py now if you do "python3 file.zip", file.zip/__main__.py will be executed, and in turn it will import file.zip/pkg/__main__.py, obtaining a result equivalent to "python -m pkg". (I still haven't figured out if the __main__.py is necessary while /importing/ a package/module from a zip file, after having added the zip file to sys.path.) So, to summarize, it seems to me that: 1) pkg/__main__.py is necessary to run "python3 -m pkg" (with -m); 2) file.zip/__main__.py is necessary to run "python3 file.zip" (without -m); 3) due to 1) and 2) creating an executable zipped package requires 2 __main__.py; 4) "python3 pkg" and "python3 -m file.zip" are not supposed to work even if the __main__.py files are in the right place. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue24632> _______________________________________