one-time factory in python for an experienced java guy

[phonky]

Hi

I have searched all over and haven't found the solution
for my problem yet. I am new to python, and all the time realize I
do program python in java, which is not great.

Besides being a real-life problem, I want to
solve it as elegant as I can, using it to
also learn about python (I know I could just
hack something easy for now).

That's what I want to do.

I have an Account class.
An Account instance has to get an account number.
On instance creation, I want the account number to
be generated (I don't want callers to pass
the account # to ensure uniqueness):

class Account(object):
def __init__(self, holder):
self.__accountnumber = self.__generate_account_number()

Now, I do not know yet how the account number scheme looks like.
For now, I just want to have an incremental number; later,
when going to production, we'll need the proper one.

Furthermore, as we plan to distribute the package, we want
to allow custom account numbering schemes. Thus, customers
should be able to plug in their own AccountNumberGenerator implementation.

For now, I have a generators.py module.

I have an AccountNumberGenerator base class,
all subclasses should implement "generate".

I have an IncrementalGenerator subclass.

So for now, I need to instantiate IncrementalGenerator,
allowing for a future module to plugin their own generator.

Any suggestions on how to do this?
Thanks so much
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Re: one-time factory in python for an experienced java guy

[phonky]

Stefan, thanks first of all


Use a global variable in the module.


I have an account_number_generator variable in the module,
I got that hint from searching the web.

But where my stubborn java mind doesn't release me:
what does the variable contain? Do I create the actual
IncrementalGenerator object there? Or the super class?
Or just a string, which a factory method takes to
create the actual object?

What I especially don't get:
How will an external module overwrite that variable?

I fail to see, python being interpreted, how I can ensure
that a future module is being executed later, thus
overwriting the variable.

Thanks again.

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Re: one-time factory in python for an experienced java guy

[phonky]

Thanks Paul,


Ugh, just forget everything you ever knew about java.  Do some Zen
exercises to erase your mind.  Then read a Python tutorial as if
you're starting from nothing.


Yeah, surely right, but easier said than done...
I'm working on it.

Taking your example.

import itertools

class Account(object):
   def __init__(self, holder, gen=itertools.count()):
  self.__accountnumber = gen.next()

If you consider my python illiteracy,

"itertools.count(): Make an iterator that returns consecutive integers 
starting with n"


to me that sounds like that solves the increment issue, but what about
future modules wanting to plug in a different
numbering format, e.g. 205434.1234 or whatever?


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Re: one-time factory in python for an experienced java guy

[phonky]

Thanks for all replies.

I need to practice much more pythonese
In fact I don't think to understand all
of your suggestions, so I'll need to
go through them and decide what approach I am going
to take.

Thanks a lot!
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