I am Java programmer. I started learning Python few days ago. I'm wondering: are there any equivalents to
map.forEach(System.out::println)
in Python with lambdas? Or only with for loop:
for e in map: print(e)
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2 Answers
There is no equivalent to Java's imperative Iterable.forEach or Stream.forEach method. There's a map function, analogous to Java's Stream.map, but it's for applying transformations to an iterable. Like Java's Stream.map, it doesn't actually apply the function until you perform a terminal operation on the return value.
You could abuse map to do the job of forEach:
list(map(print, iterable))
but it's a bad idea, producing side effects from a function that shouldn't have any and building a giant list you don't need. It'd be like doing
someList.stream().map(x -> {System.out.println(x); return x;}).collect(Collectors.toList())
in Java.
The standard way to do this in Python would be a loop:
for thing in iterable:
print(thing)
Comments
Python also has a map function and it uses the syntax map(function, iterable, ...)
See Python docs: https://docs.python.org/2/library/functions.html#map
4 Comments
Don_Quijote
But why this: a = {1, 2, 3} map(lambda x: print(x), a) - won't print anything?
Brian
See this SO question: stackoverflow.com/questions/7731213/… I hope it answers your question :)
Matthias
@Don_Quijote map returns a new list with the same number of elements as the original list. The print function does however not return something. So it is not possible to create this new list.
Matthias
@Don_Quijote you could however create a new function def custom_print(x): print(x); return x with side effects and then use map(custom_print, a) But I rather don't advise such practices