Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #197786

Re: Hack or beauty?

Show all headers | View raw

Michael F. Stemper wrote:
> I have a program that does some calculations for multiple
> different values of a certain quantity. I wanted to either
> write a second program that would hold the first quantity
> fixed and loop over a different one, or to extend the
> first to do either of those based on a command-line option.
> 
> While noodling around, I thought "what about --" and came up
> with the following idea:
> 
> ============================================================
> if options.angle:
>    angles = [0.05*k for k in range(7)]
> else:
>    comps = [0.1*k for k in range(6)]
> 
> for variable in angles if options.angle else comps:

The `angles if options.angle else comps` part evaluates to either 
`angles` or `comps` depending on the value of `options.angle`.  It's 
sometimes called a "ternary operator" because it operates on three 
values (the condition and two possible results).  If you're familiar 
with C or Java, it's similar to `options.angle ? angles : comps` (don't 
worry if you're not familiar with C/Java; just though that might help 
explain if you do happen to be).

The `for` loop then iterates over whichever of `angles` or `comps` is 
the result.  With parentheses to clarify, it's equivalent to:
```
for variable in (angles if options.angle else comps):
```

Or similar to doing:
```
values = angles if options.angle else comps
for variable in values:
```

Personally, if I were going to use a loop like this, I'd probably write 
it in one or other of those two forms so that it's clearer what it does 
for someone reading it.  Stephan noted that it at least needs the 
parentheses to work in a list comprehension which is probably because, 
in comprehensions, `if` is used (without an `else`) to select which 
items yielded by `for` are to be included.

>    if options.angle:
>      angle = variable
>    else:
>      X_C = variable * -X_L

As far as I can see, depending on `options.angle`, either `angle` or 
`X_C` is not defined.  Unless they're each set to an initial/default 
value somewhere earlier, the next line is bound to fail.

> 
>    junk = sys.stdout.write( "%4.2f  %4.3f\n" % (angle,X_C) )

Is there a reason not to just use `print("%4.2f  %4.3f" % (angle,X_C))? 
Unless `junk` is actually used later, you shouldn't need to assign the 
return value to anything.

>    # Hard part elided for clarity
> ============================================================
> 
> I was surprised to see that one could actually write a
> for-loop like that, although it tickled my inner hacker.
> 
> What I'd like to know is: Is this an egregious abuse of the
> language, or is it perfectly pythonic?
> 
> Opinions, and even violent disagreement, are solicited.

Given the number of places different code is needed depending on 
`options.angle`, I'd probably split the "hard part" (and that 
stdout.write/print) out into a separate function and do something like:

```
if options.angle:
   angles = [0.05*k for k in range(7)]
   # X_C = something
   for angle in angles:
     hard_part(angle, X_C)
else:
   # angle = something
   comps = [0.1*k for k in range(6)]
   for X_C in comps:
     hard_part(angle, X_C)

def hard_part(angle, X_C):
   sys.stdout.write("%4.2f  %4.3f\n" % (angle, X_C))
   # or:
   # print("%4.2f  %4.3f" % (angle, X_C))
   # Hard part elided for clarity
```

-- 
Mark.

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Hack or beauty? "Michael F. Stemper" <michael.stemper@gmail.com> - 2026-05-13 13:58 -0500
  Re: Hack or beauty? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-05-13 19:33 +0000
    Re: Hack or beauty? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-05-13 21:04 +0000
      Re: Hack or beauty? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-14 01:06 +0000
    Re: Hack or beauty? "Michael F. Stemper" <michael.stemper@gmail.com> - 2026-05-14 13:25 -0500
  Re: Hack or beauty? Mark Bourne <nntp.mbourne@spamgourmet.com> - 2026-05-13 21:52 +0100
    Re: Hack or beauty? "Michael F. Stemper" <michael.stemper@gmail.com> - 2026-05-14 08:06 -0500
  Re: Hack or beauty? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-13 21:37 +0000

csiph-web