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Python 3.8.0a1 is now available for testing

pythoninsider.blogspot.com

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Re: Python 3.8.0a1 is now available for testing

#21

Post by Zanni »

petercooper wrote: post #18
luhn wrote: post #2

Notably new is the assignment expressions [1]. This was quite controversial and the battle around it caused Guido to step down as BDFL [2]. I personally think it's quite a nifty feature. I often end up writing something along the lines of: result = do_something() if result: do_more(result) Now that can be expressed as: if result := do_something(): do_more(result) It definitely has the potential to be abused and reduc…

Quick question.. why is a new operator needed? A lot of languages consider regular assignments to be expression as-is, so why couldn't `if result = do_something():` work? (Genuine question, I'm intrigued what the clash is as I rarely use Python.)

To reduce the chance of creating an assignment expression when you intended a simple comparison. Yes, there's already a different operator for equality, but it's easy to mistake = for ==. Forcing you to use := makes it a deliberate act, and makes your intention clear to the reader.

Re: Python 3.8.0a1 is now available for testing

#22

Post by mixmastamyk »

amyjess wrote: post #13
luhn wrote: post #2

Notably new is the assignment expressions [1]. This was quite controversial and the battle around it caused Guido to step down as BDFL [2]. I personally think it's quite a nifty feature. I often end up writing something along the lines of: result = do_something() if result: do_more(result) Now that can be expressed as: if result := do_something(): do_more(result) It definitely has the potential to be abused and reduc…

I find it always decreases readability. I literally cannot read C code that does this, now I'm going to have to worry about encountering unreadable Python code. Edit: Also, it violates both "explicit is better than implicit" and "there should be one and only one right way to do it". It's inherently Unpythonic.

It's explicit with the new operator. The latter is true however.

Re: Python 3.8.0a1 is now available for testing

#24

Post by gigatexal »

luhn wrote: post #2

Notably new is the assignment expressions [1]. This was quite controversial and the battle around it caused Guido to step down as BDFL [2]. I personally think it's quite a nifty feature. I often end up writing something along the lines of: result = do_something() if result: do_more(result) Now that can be expressed as: if result := do_something(): do_more(result) It definitely has the potential to be abused and reduc…

Imo the former is more readable and more pythonic

Re: Python 3.8.0a1 is now available for testing

#25

Post by klodolph »

mistrial9 wrote: post #23

I am a proponent of LTS for Python 2.7x and existing libraries. This walrus operator is a fine new feature, for those that want it in Python 3.8x and beyond. Sorry, not sorry !

Isn’t Python 2.7 already LTS? If 2010-2020 doesn’t count as LTS, then what does?

Re: Python 3.8.0a1 is now available for testing

#27

Post by klodolph »

gigatexal wrote: post #24
luhn wrote: post #2

Notably new is the assignment expressions [1]. This was quite controversial and the battle around it caused Guido to step down as BDFL [2]. I personally think it's quite a nifty feature. I often end up writing something along the lines of: result = do_something() if result: do_more(result) Now that can be expressed as: if result := do_something(): do_more(result) It definitely has the potential to be abused and reduc…

Imo the former is more readable and more pythonic

I think “Pythonic” is up there as one of my least-favorite terms of all time. I think, 99% of the time, when people say “Pythonic” they should really just be quoting one of the lines from PEP 20.

Re: Python 3.8.0a1 is now available for testing

#28

Post by DaiHafVaho »

mistrial9 wrote: post #23

I am a proponent of LTS for Python 2.7x and existing libraries. This walrus operator is a fine new feature, for those that want it in Python 3.8x and beyond. Sorry, not sorry !

PyPy offers such a long-term support; they will support their Python 2.7 interpreter indefinitely. [0]

I hope that 2019 is the year of PyPy adoption, as folks get ready to leave CPython.

[0] https://morepypy.blogspot.com/2016/08/pypy-gets-funding-from...

Re: Python 3.8.0a1 is now available for testing

#29

Post by klodolph »

amyjess wrote: post #13
luhn wrote: post #2

Notably new is the assignment expressions [1]. This was quite controversial and the battle around it caused Guido to step down as BDFL [2]. I personally think it's quite a nifty feature. I often end up writing something along the lines of: result = do_something() if result: do_more(result) Now that can be expressed as: if result := do_something(): do_more(result) It definitely has the potential to be abused and reduc…

I find it always decreases readability. I literally cannot read C code that does this, now I'm going to have to worry about encountering unreadable Python code. Edit: Also, it violates both "explicit is better than implicit" and "there should be one and only one right way to do it". It's inherently Unpythonic.

I agree that it's a violation of the “one and only one” maxim, but that maxim is a bit hard to take as an absolute. I think the problem is that there are already a lot of ways to write things in Python, the biggest example that comes to mind is list comprehensions.

    outputs = [f(x) for x in inputs]
Versus:

    outputs = []
    for x in inputs:
        outputs.append(f(x))
The assignment expression lets you:

    outputs = [y for x in inputs
               if (y := f(x)) is not None]
I know that more complicated list comprehensions in Python are a bit of a sore point for some people, but I would say that they’re also inherently unpythonic, and I like them.

Re: Python 3.8.0a1 is now available for testing

#30

Post by Alex3917 »

snazz wrote: post #20
muhbags wrote: post #4

Earlier quoted context omitted.

It is definitely useful, but it severely reduces readability in my opinion. Your example is also a great example for this. The first version in way more readable than the second version with the walrus operator.

This feels very Perl-y in the example given, in that it requires that you know what yet another operator means to read code that uses it. Since Python is supposed to be “executable pseudocode” (roughly), this kind of new operator might increase the amount of learning that a beginner has to do to read others’ code. I hope that this decision does not pave the way for more like it, because it would make Python code much…

Yeah I feel like this is going to lead to another situation like with Python classes, where it's fine (and good!) to use them in libraries but generally not so good to use them in user code. The next time I update my own style guide it will probably say something like it's ok to use the walrus operator in service methods, but not in views, since views should be readable even to front end devs and PMs who don't know any Python or Django.
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