You can omit == 0 in Python because 0 is falsy like in C and add a not after the if. That gains another character
sum(x * x for x in [1,2,3,4] if not x % 2)
and it matches this Ruby 2.4.0 (which added Array#sum)
[1,2,3,4].map{|x| x.even? ? x * x : 0}.sum
You understood correctly that the point was not sheer compactness. I only wanted to provide a context to judge the Module.function syntax compared to the object.method one. The filter, map, reduce example was accidental and I'm sure there are clever ways to compact that example further in both languages.
So the pythonic way is be
reduce_function(map_function(x) for x in input if filter_condition)
I prefer to write it in the order it runs (filter -> map -> reduce) but that's it. Thanks.
I was going to comment along these lines - while functools exists, where appropriate I'd say iterators and/or list comprehensions are more pythonic. Note that if one wants to work with simple reduce functions, there's the operator module to help:
from functools import reduce
from operator import add
# I'd also say this makes for more readable code,
# documenting intent - but many will probably say that
# basic arithmetic should be clear enough:
def is_even(n): return n % 2 == 0
def square(n): return n*n
# Don't do this for summing integers, just use "sum":
reduce(add,
(square(n) for n in
range(1,5) if is_even(n)))
> 20
Note the use of range() rather than literal list - if you have a list, that should probably be passed in by name.
Anyway, the point wasn't so much bikeshedding or code golfing - just expanding on what I think is "more pythonic" take on it.
And to be clear, I'd probably prefer:
sum(x * x for x in range(1,5) if x % 2 == 0)
for this particular example. And for more complex "real world" cases, I'd probably prefer to define my "reduce" function directly ie:
def my_sum(iterator): return reduce(add, iterator)
int_sequence = range(1,5)
my_sum(square(n)
for n in int_sequence
if is_even(n))
> 20
Note that python has map and filter as built-ins, so it's also possible to do:
sum(map(lambda x:x*x,filter(lambda n:n%2==0,range(1,5))))
# Which I find rather unreadable, but gets a bit better
# without lambdas:
sum(map(square, filter(is_even,int_sequence)))
(Phew, please excuse my personal dive into new/old list-comprehension/functional python -- but at least now I'm more clear on why everyone keep adding "threading" macros/syntax to their functional languages :-)
[ed: And if one wants threading-like syntax along with some parallelization and lazy-ness in python, there's a module for that: https://github.com/EntilZha/PyFunctional
from functional import seq
(seq(range(1,5))
.map(square)
.filter(is_even)
.reduce(add)
)