On Mon, Jun 6, 2016 at 6:51 PM, Lawrence D’Oliveiro
<[email protected]> wrote:
> On Sunday, June 5, 2016 at 11:43:20 PM UTC+12, Marko Rauhamaa wrote:
>> I often experiment with different loop constructs to find the one most
>> pleasing to the eye. Working directly off iterators is quite rare but a
>> while-vs-for consideration is frequent. Also, should the stepping part
>> be in the beginning, middle or end of the loop body?
>
> It is nice to have a common, versatile looping form which can be arranged in
> different ways to suit the problem at hand. That’s why I like the C-style
> for-statement.
>
> Here’s another example
> <https://github.com/ldo/ipy_magics/blob/master/rman_magic.py>, for the
> consideration of those who don’t seem too familiar with looping:
A 500-line function? Yikes, what an eyesore. When you have to include
#end comments in order to visually match things up, that should be a
smell that your code is excessively complex. It took me a lot of
scrolling up and down just to figure out what the scopes of the
variables were.
> while True :
> while True :
> line = next(input_line, None)
> if line != None :
> if len(include_stack) == 0 :
> linenr += 1
> #end if
> break
> #end if
> if len(include_stack) == 0 :
> break
> input_line = include_stack.pop()
> #end while
> if line == None or ... line contains something special ... :
> ...
> if line == None :
> break
> ... process special line ...
> ... replace with None to indicate it’s been processed ...
> #end if
> if line != None :
> ... process regular line ...
> #end if
> #end while
def generate_lines():
nonlocal input_line
while True:
try:
# Note input_line appears to be an iterator, not a string
# as suggested by the name.
yield next(input_line)
except StopIteration:
if include_stack:
input_line = include_stack.pop()
else:
return
for line in generate_lines():
if not include_stack:
linenr += 1
if ... line contains something special ...:
... process special line ...
else:
... process regular line ...
Much simpler than the nested while loop hell above, and not a single
break needed (if you don't count the return, that is; in any case each
loop has a single exit point). I'd be tempted to refactor input_line
and include_stack into some sort of input context class and make
generate_lines a method of the class in order to avoid having those
variables be (effectively) global, but my goal was to keep this as
close to the original in design as possible.
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