Struggeling with collections

[Steven D'Aprano]

On Monday 07 March 2016 19:24, Faling Dutchman wrote:

> Hey folks,
> 
> I am just starting off in python, but have good knowledge of both Java and
> C#. Now is the problem that I need to have multiple instances of one
> dictionary, that is not a problem if you know how many, but now, it is an
> unknown amount.

Whenever you have an unpredictable number of some object, *any* object, you 
should turn to a list, or a dict.

"I need some integers, but I don't know if there will be 3 or 5."

Wrong solution:

a = 23
b = 24
c = 25
if foo:
    d = 26
    e = 27
# later...
if foo:
    print(a, b, c, d, e)
else:
    print(a, b, c)    



Right solution:


integers = [23, 24, 25]
if foo:
    integers.extend([26, 27])
# later...
print(*foo)


It doesn't matter whether you are dealing with ints, floats, strings, dicts, 
lists, sets, or your own custom-built objects. If you don't know in advance 
how many you want, put them in a list. Or a dict.



> Some background info:
> 
> I am making a library for an API. This library must be easy to use for the
> people who are going to use it. 

Define "easy to use".



> If I do this:
> 
> class Item:
>     def __init__(self, id, productId, quantity, pageCount, files, option,
>     metadata):
>         self.id = id
>         self.productId = productId
>         self.quantity = quantity
>         self.pageCount = pageCount
>         self.files = files
>         self.option = option
>         self.metadata = metadata
> 
> itm = Item(1,None,1,1,'asdf',{'asdf': 3, 'ads': 55},None)
> print(itm)
> 
> it prints: <__main__.Item object at 0x02EBF3B0>
> 
> So that is not usefull to me.

Then create a better __repr__ or __str__ method. All you are seeing is the 
default representation inherited from object. If you don't like it, override 
it.



-- 
Steve