Python is DOOMED! Again!

Steven D'Aprano steve+comp.lang.python at
Thu Jan 22 08:23:25 CET 2015

Ethan Furman wrote:

> On 01/21/2015 08:30 PM, Steven D'Aprano wrote:
>> So what is this unspeakable, nightmarish, cryptic abomination going to
>> look like? Here's an example from PEP 484:
>> def greeting(name: str) -> str:
>>     return 'Hello ' + name
>> I don't know about you, but I think anyone who cannot read that and
>> intuit that argument `name` is a string and the return result is also a
>> string
> There is nothing inherently intuitive about that syntax.  

Strictly speaking, you are correct: the only truly intuitive interface is 
the nipple. Nevertheless, we often informally describe something as 
"intuitive" when we mean the meaning can be guessed or derived from context.

> The : makes it
> look like a dictionary (but it isn't) and the -> looks like a pointer to
> something (but it isn't).

I think you're over-thinking it from the perspective of a programmer with 
lots of experience. Think of it as pseudo-code seen from the perspective of 
somebody who doesn't know about dicts and pointers.

Arrows are common symbols for directions, flow of time, and results:

    Work hard --> Save $$$ --> Buy a new car!!!

It's not hard to jump to the conclusion that -> introduces the return 

As for colons, don't think of "dict", think of "mapping". Colons in this 
case map argument name to argument type.

The point isn't that there are no other alternative interpretations 
possible, or that annotations are the only syntax imaginable, but that 
they're not hard to guess what they mean, and if you can't guess, they're 
not hard to learn and remember.


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