Eric Snow added the comment:
Things are working as they should here. The key points:
* when running a script, sys.path[0] is set to the script's directory (with no
script sys.path[0] is set to the CWD, see issue13475),
* pkg/tests/__init__.py is loaded and executed twice: once as the script under
the __main__ module and once during import as pkg.tests,
* Python does not handle circular imports very well,
* bad things happen when a "top-level" module has the same name as a module in
the stdlib.
Together those explain what's going on. The import you did at the REPL
happened with '' at sys.path[0], so modules are found at the right relative
places: pkg, pkg.http, pkg.tests, and pkg.tests.http. There is no script
involved, just imports, so no double-loading happens.
Things go south when you run "PYTHONPATH=. python3 pkg/tests/__init__.py".
First of all, pkg/tests/__init__.py is executed twice: once as the script and
once under import. Though you set PYTHONPATH, sys.path[0] is set to
"pkg/tests", the directory the script is in. sys.path[1] is ".", what you were
expecting to be at sys.path[0]. So when finding modules, the import system
will first look in "pkg/tests" then in ".". Thus the pkg.* imports work as
expected. However, "from http.client import HTTPConnection" in
pkg/tests/http.py finds the same http.py (this time as the "http" module
instead of "pkg.tests.http") in pkg/tests rather than the stdlib module as you
expected. So it tries to import it a second time with a different module name.
Since pkg/tests/http.py is already being loaded due to pkg/test/__init__.py,
you get a circular import. Even if you did not get the circular import you
would have gotten an ImportError for "http.client" since pkg/tests/http.py
neither behaves li
ke a package nor actually has any "client" submodule.
Part of the fix is to use relative imports where appropriate. For instance,
change pkg/tests/__init__.py like this:
from . import http
Also, don't run pkg/tests/__init__.py directly. Instead try this:
PYTHONPATH=. python3 -m pkg.tests
However, this implies that you wanted to run the package as a script, so you
should have pkg/tests/__main__.py which would import pkg.tests. Alternately,
you could have a dedicated script elsewhere, perhaps next to the pkg directory
that does the same thing. Here's what I mean:
some_project/
pkg/
tests/
__init__.py
__main__.py (option 1)
http.py
__init__.py
run_unittests.py (option 2)
Finally, don't name your modules with the same names as those in the stdlib.
<wink>
----------
nosy: +eric.snow
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<http://bugs.python.org/issue16570>
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