On 2020-04-10 5:21 p.m., Elliott Dehnbostel wrote:
Hello Everyone,

If I've done this incorrectly, please let me know so that I can improve/revise. I'm new to the Python community and quite enjoy the more functional features of Python 3, but have I have a peeve about it. I'd like to propose and discuss the following enhancement to Python 3:

Consider the following trivial for-loop:
chars = "abcaaabkjzhbjacvb"
seek = {'a','b','c'}
count = 0
for a in chars:
     if a in seek:
          count += 1
  
Gross. Twice nested for a simple count.
We could refactor the block like so:
chars = "abcaaabkjzhbjacvb"
seek = {'a','b','c'}
count = 0
for a in filter(lambda c: c in seek, chars): count += 1
Which is all well and good, but doesn't quite read like English. It's verbose, too.
It also uses advanced concepts new programmers may not understand.
We could do this:
chars = "abcaaabkjzhbjacvb"
seek = {'a','b','c'}
count = sum([1 for a in chars if a in seek])
However, this changes important semantics by creating an entire new list before summing.
Also, adding just one more expression to the most nested block thwarts that refactor.
I propose the following enhancement:
chars = "abcaaabkjzhbjacvb"
seek = {'a','b','c'}
count = 0
for a in chars if a in seek: count += 1

fwiw you got pretty close to these there:

sum(1 for a in chars if a in seek) # is valid

for a in (a for a in chars if a in seek): count += 1 # is also valid (but ugly)

What happened there?
I've allowed a condition to follow the "for" construct without a colon or newline between.
To be clear, this remains incorrect:
chars = "abcaaabkjzhbjacvb"
seek = {'a','b','c'}
count = 0
for a in chars # No colon prior to the newline
     if a in seek:
          count += 1
Value proposal:
I assert that the inlined 'if' condition pattern is superior to the alternative refactors.
Right now, the way to acquire an invariant in a more nasty loop would be:
for a in iterable:
     if condition:
          continue
But this is messy and not particularly Pythonic.
The filter approach uses concepts that should not be necessary for this task.
The comprehension approach has different, undesirable semantics.
Conclusion:
I wanted to submit my thoughts here before getting too deep into this. Any input would be appreciated!
Thanks everyone.
  



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