max2 at fisso.casa
Thu Mar 31 17:55:58 CEST 2005
Peter Hansen wrote:
> max(01)* wrote:
>> hi everybody.
>> suppose that code-1.py imports code-2.py and code-3.py (because it
>> uses names from both), and that code-2.py imports code-3.py.
>> if python were c, code-1.c should only *include* code-2.c, because the
>> latter in turns includes code-3.c.
>> inclusion of modules in c is a purely preprocessing textual matter
>> (compilation is deferred to after the fact), i guess, so that such
>> things are possible. import of modules in python is a different beast,
>> so the "redundancy" is (i think) necessary.
>> any comment/suggestion/idea?
> You're mixed up about this whole idea.
that's why i am asking for advice here.
> You say first that "[code-1] uses names from both",
> which by definition means that it needs to import
> both. (I say by definition because import is *how*
> a module gets names from another module.)
> Then you say that code-1 can choose not to include
> code-3 because some other module is including it...
> but so what? That doesn't change the fact that
> code-1 needs names from code-3, and just because
> code-3 is imported elsewhere is no reason to think
> that code-1 magically gets its names too. Should
> all modules magically see all names in all modules
> which are imported, even by other modules?
that's how inclusion works in c, which is why i asked for clarification
about the differences between c-style includes and python-style imports.
now i can see that python-style import is more like the inclusion of
declarations in c (the "names"), usually shipped as *.h header files.
the real *definition* of names is python (contents of variables,
definition of functions, and so on) i guess is inserted later in the
process of execution.
> would pretty much defeat most of the value of
> Anyway, why this concern over so-called redundant
> imports? The source code itself is not parsed
> and compiled all over again, and even the .pyc file
> is not re-read... once any module has imported a
> module any other import just retrieves a reference
> to that module from the sys.modules dictionary,
> which is practically a free operation.
my concern was motivated by a (clumsy) attempt to understand the
difference of mechanism between the approach to modular programming in a
more "traditional" language (c) and python.
thanks again for your couseling.
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