[Python-Dev] PEP 8 modernisation

Nick Coghlan ncoghlan at gmail.com
Fri Aug 2 11:10:19 CEST 2013

On 2 Aug 2013 17:31, "Alexander Shorin" <kxepal at gmail.com> wrote:
> Hi Terry,
> On Fri, Aug 2, 2013 at 12:29 AM, Terry Reedy <tjreedy at udel.edu> wrote:
> > def f(x): return 2*x
> > f = lambda x: 2*x
> > Three spaces is seldom a crucial difference. If the expression is so
long it go past the limit (whatever we decide it is), it can be wrapped.
> and if I have multiple lambda-like def`s it will hit the PEP rule :
> > While sometimes it's okay to put an if/for/while with a small body on
the same line, never do this for multi-clause statements. Also avoid
folding such long lines!
> On Fri, Aug 2, 2013 at 12:29 AM, Terry Reedy <tjreedy at udel.edu> wrote:
> >> and/or to remove duplicates (especially for sorted groupby case)?
> > I do not understand this.
> See [Python-Dev] Lambda [was Re: PEP 8 modernisation] thread for example:
> http://mail.python.org/pipermail/python-dev/2013-August/127715.html
> On Fri, Aug 2, 2013 at 12:35 AM, Terry Reedy <tjreedy at udel.edu> wrote:
> >> I understand this, but I'm a bit confused about fate of lambdas with
> >> such guideline since I see no more reasons to use them with p.9
> >> statement: long lines, code duplicate, no mock and well tests etc. -
> >> all these problems could be solved with assigning lambda to some name,
> >> but now they are looks useless (or useful only for very trivial cases)
> >
> >I do not understand most of that, but...
> >The guideline is not meant to cover passing a function by parameter
name.  mylist.sort(key=lambda x: x[0]) is still ok. Does "Always use a def
statement >instead of assigning a lambda expression to a name." need 'in an
assignment statement' added?
> I wrote about that lambda`s use case become too small to use them in
> real code. If they are dishonoured - need to write so and clearly, but
> not limiting their use cases step by step till every Python devs will
> think like "Lambdas? Why? Remove them!".

Lambda was almost removed in Python 3.

> Using `dict` to store lambdas:
> > op = { 'add': lambda x,y: x*y, 'mul':  lambda x, y: x+y}
> Shows the hack to bypass PEP8 guides. Do you like to see code above
instead of:
> add = lambda x,y: x*y
> mul = lambda x, y: x+y
> Probably, I don't since dict is a blackbox and I have to check things
> first before use them.

People are free to write their own style guides that disagree with pep 8 (a
point which is now made explicitly in the PEP).

> Disclaimer:  I don't try to stand for lambdas, I'm not using them
> everywhere in my code, but I'd like to know answer for the question
> "Why lambdas?". Currently, it is "Handy shorthand functions - use them
> free", but with new PEP-8 statement I really have to think like
> "Lambdas? Really, why?".

Use them for an anonymous function as an expression. All PEP 8 is now
saying is that giving a lambda a name is to completely misunderstand what
they're for.

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