Re: [Python-ideas] JavaScript-Style Object Creation in Python (using a constructor function instead of a class to create objects)

On Tue, May 16, 2017 at 5:04 PM, Guido van Rossum gvanrossum@gmail.com wrote:

What features of attrs specifically solve your use cases? > (not Stephen)

I hadn’t thought about this use case:

In [1]: class C(): ...: x = 1 ...: ...: def __init__(self, x=None): ...: if x is not None: ...: self.x = x ...: ...: def __str__(self): ...: return 'C(%s)' % self.x ...:

In [2]: c1 = C() ...: c2 = C(2) ...:

In [3]: print(c1, c2) C(1) C(2)

And I might use it here on.

What I like about attrs is:

• The class level declaration of instance attributes
• That the reasonable init, repr, and eq are generated

I don’t like the excessive wordiness in attrs, and I don’t need “the kitchen sink” be available to have instance attributes declared at the class level. A solution based on the typing module would be much better.

Basically, Python is lacking a way to declare instance fields with default values away of the initializer. Several of the mainstream OO languages (Java, Swift, Go) provide for that.

I haven’t thought much about this, except about if there’s indeed a need (and there is), but I can’t know if the solution if through decorators, or inheritance.

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Juancarlo Añez