OT: Addition of a .= operator

[dn]

On 24/05/2023 12.27, Chris Angelico wrote:
> On Wed, 24 May 2023 at 10:12, dn via Python-list <python-list at python.org> wrote:
>> However, (continuing @Peter's theme) such confuses things when something
>> goes wrong - was the error in the input() or in the float()?
>> - particularly for 'beginners'
>> - and yes, we can expand the above discussion to talk about
>> error-handling, and repetition until satisfactory data is input by the
>> user or (?frustration leads to) EOD...
> 
> A fair consideration! Fortunately, Python has you covered.
> 
> $ cat asin.py
> import math
> 
> print(
>      math.asin(
>          float(
>              input("Enter a small number: ")
>          )
>      )
> )
> $ python3 asin.py
> Enter a small number: 1
> 1.5707963267948966
> $ python3 asin.py
> Enter a small number: 4
> Traceback (most recent call last):
>    File "/home/rosuav/tmp/asin.py", line 4, in <module>
>      math.asin(
> ValueError: math domain error
> $ python3 asin.py
> Enter a small number: spam
> Traceback (most recent call last):
>    File "/home/rosuav/tmp/asin.py", line 5, in <module>
>      float(
> ValueError: could not convert string to float: 'spam'
> 
> Note that the line numbers correctly show the true cause of the
> problem, despite both of them being ValueErrors. So if you have to
> debug this sort of thing, make sure the key parts are on separate
> lines (even if they're all one expression, as in this example), and
> then the tracebacks should tell you what you need to know.


Yes, an excellent example to show newcomers to make use of 'the 
information *provided*' - take a deep breath and read through it all, 
picking-out the important information...


However, returning to "condense this into a single line", the 
frequently-seen coding is (in my experience, at least):

     quantity = float( input( "How many would you like? " ) )

which would not produce the helpful distinction between 
line-numbers/function-calls which the above (better-formatted) code does!


Summarising (albeit IMHO):

- if relatively trivial/likely to be well-known: collect the calls into 
a chain, eg

     user = user.strip().lower()

- otherwise use separate lines in order to benefit from the stack-trace

- (still saying) use separate assignments, rather than chaining more 
complex/lesser-known combinations

- ensure that the 'final' identifier is meaningful (and perhaps the 
first, and/or even an 'intermediate' if pertinent or kept for re-use later)

- perhaps re-use a single identifier-name as a temp-variable, if can 
reasonably 'get away with it'
(and not confuse simple minds, like yours-truly)


-- 
Regards,
=dn