python classes

[Peter Otten]

William D. Gill wrote:

> I'm new to python and am probably trying too many new things at once, but
> here goes.

Welcome!

> I am working with a (MySQL) database and am trying to make a html /python
> interface for editing records.
> Data is broken up into several tables, and related by customer number. 
> For example one table contains basic information about the customer, one
> table phone numbers (one record for published number, one for cell phone,
> etc, all customers will have at least one record here).
> 
> I want to use python classes in my code so I have a couple of  questions
> about python classes:
> 
> 1) can a class __init__ have multiple "signatures like in C++  i.e.
> MyClass( int, string), . MyClass(int) ?

No, but you can provide defaults:

>>> class MyClass:
...     def __init__(self, mandatory, value=99, name="unknown"): pass
...
>>> MyClass(1)
<__main__.MyClass instance at 0x40290aec>
>>> MyClass(1,2)
<__main__.MyClass instance at 0x40290a6c>
>>> MyClass(1, name="whoever")
<__main__.MyClass instance at 0x40290a4c>

and so on ad infinitum.

> 2) can a class attribute be an instance of another class ...

Yes, it can.

> or is multiple inheritance the proper answer?

If the _question_ is 42?, then I would say so :-)

> 3) Can I make instantiation fail if an invalid customer number is use, and
> wrap the "a=MyClass(cusid=999) in an exception?

You _should_ raise a custom exception (just derive from Exception) which can
be loaded with arbitrary information - in your example that would rather be
the bad customer id than the inconsistant MyClass instance.


Peter