On Fri, Sep 13, 2013 at 6:50 PM, Dhananjay Nene <dhananjay.n...@gmail.com> wrote: > On Fri, Sep 13, 2013 at 3:58 PM, Saager Mhatre <saager.mha...@gmail.com> > wrote: >> 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] > > Nice. I reached out for the "Favourite" button but realised > emails/mailing lists don't have it. > > I do think it can be a little easier to understand by doing > s/package-module/namespace/g. Having done that I realised a few things > needed to be reworded, and then noticed a few minor corrections were > required. > > Here's the result (Have attempted to only make minor structural > corrections without adjusting any of the opinions or rationale > expressed herein) > --------------------------------------------------------------------------------------------------------- > 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 namespace is a dict-like object that binds names to values. > * A namespace is an abstract notion, which is implemented as packages or > modules > Thus a package is-a namespace and a module is-a namespace > * The package namespace includes the modules in it and the stuff in > __init__.py > > I guess it'd be easier to explain with with an example. > > Semantically... > --- > * Lets stick to json.tool. In this case, json is a package and tool is > a module > * They are both namespaces in that each can contain bindings to names > => json.dump and tool.main. > * json is a package namespace 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 part of the package namespace, > i.e., ie. it has the 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 packages as namespaces, > because sub-modules do not end up as names in the package namespace > 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*
Apologies : that was an incomplete paste .. here's a continuation ----------------------------------- >>> 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 > > > > -- > ---------------------------------------------------------------------------------------------------------------------------------- > http://blog.dhananjaynene.com twitter: @dnene google plus: > http://gplus.to/dhananjaynene -- ---------------------------------------------------------------------------------------------------------------------------------- http://blog.dhananjaynene.com twitter: @dnene google plus: http://gplus.to/dhananjaynene _______________________________________________ BangPypers mailing list BangPypers@python.org https://mail.python.org/mailman/listinfo/bangpypers
