[Tutor] How does one construct a module for import?

[Steven D'Aprano]

On Mon, Jun 02, 2014 at 01:21:29PM +0100, Sydney Shall wrote:
> I am having a similar problem.

Actually, I don't think so. Your problem doesn't appear to have anything 
to do with the problem that Charles Agriesti is having. The only 
connection seems to be that you are both using Python. Read on for more 
details.


> I have now worked out how to copy my helper file to the correct 
> location, in my case is:
> '/Users/sydney/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages'
> 
> When I type the following at the IPython prompt I get no error message;
> import findGraphParametersV2

Right. This says that, unlike Charles' situation, in your case Python is 
correctly importing your module. You may have a problem, but *importing* 
is not the problem.


> And the following led me to believe all was well.
> 
> I type in the following:
> In [19]: dir(findGraphParametersV2)
> 
> Out[19]:
> ['__builtins__', '__doc__', '__file__', '__name__', '__package__',
>  'findGraphParameters', 'np', 'pylab']

This shows that the findGraphParametersV2 (whew, that's a mouthful!) 
module has eight attributes. Some of them (like __name__) are created 
automatically by Python. Others, like np and pylab, are probably created 
when your module imports other modules. The one that you probably care 
about is findGraphParameters, which you need to call using:

    findGraphParametersV2.findGraphParameters( arguments )

Notice that you need to give the module name first, followed by the name 
of the thing inside the module.

 
> However, when I use the import statement in my program I get a runtime 
> error as follows:

Just a moment. A couple of sentences ago, you said that importing works. 
Now you say it doesn't. Which is it?

Please be more specific about the code you are running. Unfortunately, 
while we know Python quite well, we're not very good at reading your 
mind, and we can't see your code. You need to identify what line of code 
is being run, and tell us.

If the code is:

    import findGraphParametersV2

which then fails with ImportError, that tells us some valuable 
information. If the code is:

    result = findGraphParametersV2(some, arguments, here)

which then fails with the error you mentioned:

    TypeError: 'module' object is not callable

that tells us something completely different! Both the type of the 
exception (ImportError, TypeError) and the error message are important, 
but equally important is what you did that resulted in the error.


> <ipython-input-14-abb1b897e8b9> in <module>()
> ----> 1 CapitalSimulation(51, 4000.0, 20.0, 20.0, 100, 1.0, 0.0, 40.0, 1.0)
> 
> /Users/sydney/My_Documents/Political_Economy/Capital_Simulation/Capital/Current 
> version/CapitalWithProdV14.py in CapitalSimulation(number_of_cycles, 
> capital_advanced, unit_constant_capital, wagerate, labour_powers, 
> productivity, prodinc, work_duration, labour_intensity)


If I am reading this correctly, this has absolutely nothing to do with 
the findGraphParametersV2 module or the findGraphParameters function 
inside that module. It looks to me like you have a *different* module, 
called CapitalSimulation, and you try to call it as if it were a 
function.

It is difficult to tell exactly what is going on, but my guess is that 
inside the CapitalSimulation module you have a function *also* called 
CapitalSimulation. So in your module CapitalWithProdV14 (that's the 
THIRD module!!!) you probably have some code like:

import CapitalSimulation  # this is a module, not a function

CapitalSimulation(number_of_cycles, capital_advanced, blah blah blah...)


That second line is the problem. You need to change it to:

CapitalSimulation.CapitalSimulation(number_of_cycles, ...)


I think. Like I said, without understanding your code, it's difficult to 
be sure exactly what's going on.


Reading between the lines, I feel that perhaps somebody has told you 
that you should have one class or one function per file. Or perhaps you 
have been reading Java programming books. Either way, it seems to me 
that you have an excess of modules and too many confusing imports. That 
way leads to frustration.

I believe that you will be much better served to have *one* file per 
project, rather than splitting your project into a dozen itty bitty 
files. That way you don't need to care about importing your own modules, 
because everything is already inside the one file. 

If you *must* have separate files, never never never (well, almost 
never) give them the same name as the class or function inside them. A 
good convention is to name the module in all lower case, and the class 
in InitialCaps:

# no, too confusing
CapitalSimulation.CapitalSimulation(...)

# better
capital_simulation.CapitalSimulation(...)


That way, you can tell at a glance which is the module and which is the 
class inside the module, and if you make a mistake, it will be more 
easily understood:

capital_simulation(...)  # wait a second, that's a module!


[...]
> I do not really understand what Steven is recommending below.
> Is it an init statement in a file or is it an independent file.

I don't believe this has anything to do with your problem, but for the 
record, there is no init statement in Python (although classes do have 
an __init__ method). I suggested to Charles that he add an empty 
__init__.py file inside his project folder. That would make it an 
separate file.


Good luck!



-- 
Steven