[Python-Dev] Re: Type annotations, PEP 649 and PEP 563

2021-10-26 Thread Larry Hastings 


On 10/26/21 5:22 PM, Bluenix wrote:

* Functions having the same signature share the same annotation tuple.

Is this true with code that have a mutable default?
[... examples deleted...]



You're confusing two disjoint concepts.

First of all, all your examples experiment with default values which are 
unrelated to their annotations.  None of your examples use or examine 
annotations.


Second, Inada-san was referring to the tuple of strings used to 
initialize the annotations for a function when PEP 583 (stringized 
annotations) is active.  This is a clever implementation tweak that 
first shipped with Python 3.10, which makes stringized annotations very 
efficient.  Since all the names and annotations are strings, rather than 
creating the dictionary at function binding time, they're stored in a 
tuple, and the dictionary is created on demand.  This tuple is a 
constant object, and marshalling a module automatically collapses 
duplicate constants into the same constant.  So identical PEP 583 
annotation tuples are collapsed into the same tuple.  Very nice!



//arry/

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[Python-Dev] Re: Type annotations, PEP 649 and PEP 563

2021-10-26 Thread Bluenix 
> * Functions having the same signature share the same annotation tuple.

Is this true with code that have a mutable default?

>>> def a(arg = []):
... arg.append('a')
... return arg
...
>>> def b(arg = []):
... arg.append('b')
... return arg
...
>>> a()
['a']
>>> a()
['a', 'a']
>>> a()
['a', 'a', 'a']
>>> b()
['b']
>>> b()
['b', 'b']
>>> b()
['b', 'b', 'b']
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