Python: Quick and dirty datatypes (DTO)

Question

Very often, I find myself coding trivial datatypes like

class Pruefer:
    def __init__(self, ident, maxNum=float(\'inf\')         


        

Answer 1

I don't have much to add to the already excellent answer by Alexey Kachayev -- However, one thing that may be useful is the following pattern:

Pruefer.__new__.func_defaults = (1,float('inf'),"")

This would allow you to create a factory function which returns a new named-tuple which can have default arguments:

def default_named_tuple(name,args,defaults=None):
    named_tuple = collections.namedtuple(name,args)
    if defaults is not None:
        named_tuple.__new__.func_defaults = defaults
    return named_tuple

This may seem like black magic -- It did to me at first, but it's all documented in the Data Model and discussed in this post.

In action:

>>> default_named_tuple("Pruefer", "ident maxNum name",(1,float('inf'),''))

>>> Pruefer = default_named_tuple("Pruefer", "ident maxNum name",(1,float('inf'),''))
>>> Pruefer()
Pruefer(ident=1, maxNum=inf, name='')
>>> Pruefer(3)
Pruefer(ident=3, maxNum=inf, name='')
>>> Pruefer(3,10050)
Pruefer(ident=3, maxNum=10050, name='')
>>> Pruefer(3,10050,"cowhide")
Pruefer(ident=3, maxNum=10050, name='cowhide')
>>> Pruefer(maxNum=12)
Pruefer(ident=1, maxNum=12, name='')

And only specifying some of the arguments as defaults:

>>> Pruefer = default_named_tuple("Pruefer", "ident maxNum name",(float('inf'),''))
>>> Pruefer(maxNum=12)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: __new__() takes at least 2 arguments (2 given)
>>> Pruefer(1,maxNum=12)
Pruefer(ident=1, maxNum=12, name='')

Note that as written, It's probably only safe to pass a tuple in as defaults. However, you could easily get more fancy by ensuring you have a reasonable tuple object within the function.