problem with curring in python

[Peter Otten]

Antoon Pardon wrote:

> On 22/10/19 12:02, Terry Reedy wrote:
>> On 10/22/2019 4:58 AM, Antoon Pardon wrote:
>>> Using python 3.5
>>>
>>> I have been experimenting with curried functions. A bit like in Haskell.
>>> So I can write the following function:
>>>
>>> def sum4(a, b, c, d):
>>> return a + b + c + d
>>>
>>> summing = curry(sum4)
>>>
>>> print summing(1)(2)(3)(4) # this prints 10.
>>>
>>> The problem is I need the signature of the original function in order to
>>> know when to finally call the function and return the actual result.
>>> However buildin functions don't have a
>>
>> I believe most do.
> 
> Well I may have jumped to my conclusion, but those in operator don't seem
> to have a signature.
> 
>>>> inspect.signature(operator.mul)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "/usr/lib/python3.5/inspect.py", line 2988, in signature
>     return Signature.from_callable(obj, follow_wrapped=follow_wrapped)
>   File "/usr/lib/python3.5/inspect.py", line 2738, in from_callable
>     follow_wrapper_chains=follow_wrapped)
>   File "/usr/lib/python3.5/inspect.py", line 2231, in
>   _signature_from_callable
>     skip_bound_arg=skip_bound_arg)
>   File "/usr/lib/python3.5/inspect.py", line 2061, in
>   _signature_from_builtin
>     raise ValueError("no signature found for builtin {!r}".format(func))
> ValueError: no signature found for builtin <built-in function mul>
> 

New in Python 3.7:

$ python3.5 -c 'from operator import mul; print(mul.__text_signature__)'
None
$ python3.6 -c 'from operator import mul; print(mul.__text_signature__)'
None
$ python3.7 -c 'from operator import mul; print(mul.__text_signature__)'
($module, a, b, /)