Sergey Dorofeev wrote: > > "Peter Otten" <[EMAIL PROTECTED]> wrote in message > news:[EMAIL PROTECTED] >>>>> Please help, is there way to use sub-expressions in lambda? >>>>> For example, if I want to calculate sin(x^2)+cos(x^2) I must code: >>>>> lambda x: sin(x*x)+cos(x*x) >>>>> How to make x*x to be evaluated once? >>>> >>>>>>> (lambda x: [sin(x2) + cos(x2) for x2 in [x*x]][0])(.5) == sin(.5*.5) >>>>>>> + >>>> cos(.5*.5) >>>> True >>>> >>>> The real answer is of course: Use a function. >>> >>> But what about something like >>> >>> lambda x: sin(y)+cos(y) where y=x*x >>> >>> ? >>> May be this could be a PEP? If there is no straight way to do this. >> >> def f(x): >> y = x*x >> return sin(y) + cos(y) >> >> What is not straightforward about that? > > This code is needed once in a map,
Perhaps you like [sin(y)+cos(y) for y in (x*x for x in items)] then. > so I don't want 3+ extra lines. What syntax would you suggest for a lambda enhanced to cover your use case? I suppose you will end up with roughly the same number of characters, all crammed in one line -- or broken into lines at a random position as it happens with overambitious list comprehensions. > Solution seemed so simple... It /is/ simple. > I always considered python as languague, where simple things do not > require extensive coding. In Python, when conciseness and readability compete, readability tends to win (with the inline if...else as a notable exception). > Moreover, this construction is common thing in functional programming. I can write Haskell in any language :-) Peter -- http://mail.python.org/mailman/listinfo/python-list
