RFC: For Loop Invariants

[Terry Reedy]

On 4/10/2020 4:44 PM, Elliott Dehnbostel wrote:

> chars = "abcaaabkjzhbjacvb"
> seek = {'a','b','c'}
> count = 0for a in chars:
>       if a in seek:
>            count += 1

Why did you repeatly omit the \n after 0?  Please paste code that ran

> Gross. Twice nested for a simple count.

Twice indented does not particularly bother me.

 > [snip]
> *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.

Unnecessary.  Use a generator comprehension (expression).

sum(1 for a in chars if a in seek)

> chars = "abcaaabkjzhbjacvb"
> seek = {'a','b','c'}
> count = 0  # fixed
> for a in chars if a in seek: count += 1

Rejected and rejected again, any mixing of keyword clauses like this 
except in comprehensions.  The sum expression is shorter and only 1 line.

-- 
Terry Jan Reedy