[Python-Dev] PEP 8: Discourage named lambdas? (original) (raw)

Steven D'Aprano steve at pearwood.info
Sun May 4 11:36:50 CEST 2008

On Sat, 3 May 2008 08:27:27 pm Nick Coghlan wrote:

Samuele Pedroni wrote: > I found only an example in my personal recent code: > > START = "" > END = "" > TITLEPATTERN = lambda s: "%s" % s > > this three are later used in a very few .find() and .replace() > expressions in the same module. I suppose my point is that while I > agree it should be discouraged and is really silly to do it for the > few chars gain, it can be used to some effect in very rare cases.

The way that's written currently, I think I could very easily miss the fact that TITLEPATTERN is a callable while glancing over the code (and be very confused if I later saw it being called or passed as a callback).

I think you're exaggerating a tad here. Why would you be "very confused" when you see TITLEPATTERN() or foo(callback=TITLEPATTERN)? What else would TITLEPATTERN be but a callable when it's being used as a callable?

Converting to a def makes it obvious that one of these lines is not like the others:

Do you get confused by factory functions?

(or for that matter callable class instances, types, etc.)

TITLEPATTERN = factory(args) # note the lack of def ... lots of code ... foo(callback=TITLEPATTERN) # Note: TITLEPATTERN is a callable

I think that if I argued that factory functions were bad because "I think I could very easily miss the fact that TITLEPATTERN is a callable while glancing over the code (and be very confused if I later saw it being called or passed as a callback)", most people would dismiss the concern and tell me it was my problem. It certainly isn't a good reason for discouraging factory functions, and I don't think it should be considered a good reason for discouraging lambdas.

-- Steven D'Aprano

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