On Fri, Sep 13, 2013 at 1:10 PM, Saju M <sajup...@gmail.com> wrote: > Saager, > > As per python module-import semantics, sub-modules don't end up as names > in the > package-module[*] unless explicitly added. > > I didn't get it, what you mean by package-module[*] ?. >
Ah, there it is... the sound of your head exploding! :P Buckle up, this is going to be a fast, but rough ride! Basically... ---- * A module is a dict-like object that binds names to values. * A package is a namespace that can contain (only) other modules (which could, in turn, be package-modules themselves). * A package-module[1] would be a module that also serves as a package. I guess it'd be easier to explain with with an example. Semantically... --- * Lets stick to json.tool. In this case, json is a module and tool is a sub-module of the json module. * They are both modules in that each can contain bindings to names => json.dump and tool.main. * But, json is also a package in that it contains the tool module => json.tool * The sub-module relationship is mostly evident from the fact that the tool module is referenced by prefixing 'json.' to it => import json.tool; * Or providing 'json' as the package to look for the module => from json import tool Physically... --- * Any .py file can be loaded as a module. * Any directory with an __init__.py file can be treated as a package. * The __init__.py file itself serves as the package-module, i.e., the module with same name as the package * Any .py files inside the directory (except __init__.py, of course) can be loaded as sub-modules of the above package. * Any sub-directories inside the directory (containing __init__.py, of course) can be loaded as sub-packages of the above package. * Turtles all the way... Funda-mentally... --- * The confusion basically stems from the fact that Python chose to conflate physical storage and namespacing with just enough overlap to be inconsistent. * They are conflated in that package/module naming and their lookup (finding the code for a module) is tied to the physical storage hierarchy. * They are inconsistent that module loading is transitive only upwards in the hierarchy, i.e., when you load a module, all packages above it in the hierarchy are automatically loaded.[2] * However, sub-modules are not loaded even though the physical hierarchy evidences it. * The conflation extends further as we look as modules as namespaces, because sub-modules do not end up as names in package-modules until they are loaded; see below Python 2.7.4 (default, Apr 19 2013, 18:28:01) [GCC 4.7.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. *>>> json* Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'json' is not defined *>>> import json* *>>> json* <module 'json' from '/usr/lib/python2.7/json/__init__.py'> *>>> json.tool* Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'module' object has no attribute 'tool' *>>> from json import tool* *>>> json* <module 'json' from '/usr/lib/python2.7/json/__init__.py'> *>>> tool* <module 'json.tool' from '/usr/lib/python2.7/json/tool.py'> *>>> json.tool* <module 'json.tool' from '/usr/lib/python2.7/json/tool.py'> *>>> * Finally... --- On a closing note, it goes without saying that these packages are not to be confused with packages as published on package indexes such as https://pypi.python.org.[3] (steps behind transparent blast shield to calmly enjoy the sight of more exploding heads) - d [1] I don't believe it would be entirely in the best interest of either of our healths to use this term outside of this thread! [2] IIRC, this was not true for python <2.5 (I think); I recall hitting some really weird import errors when running newer code on a really old interpreter when it suddenly couldn't reference the packages that a loaded module belonged to until they were explicitly loaded. [3] To those in the know, I would be tremendously obliged if you could tell me what brand of blow they were using when they came up with this byzantine, labyrinthine nomenclature and related implementation. I bet it was, as they say, "like, totally radical dude!" _______________________________________________ BangPypers mailing list BangPypers@python.org https://mail.python.org/mailman/listinfo/bangpypers
