Print doesn't print when it's in map, Python
Python 3.xDictionaryPython 3.x Problem Overview
primes = [2,3,5,7..] (prime numbers)
map(lambda x:print(x),primes)
It does not print anything. Why is that? I've tried
sys.stdout.write(x)
too, but doesn't work either.
Python 3.x Solutions
Solution 1 - Python 3.x
Since lambda x: print(x) is a syntax error in Python < 3, I'm assuming Python 3. That means map returns a generator, meaning to get map to actually call the function on every element of a list, you need to iterate through the resultant generator.
Fortunately, this can be done easily:
list(map(lambda x:print(x),primes))
Oh, and you can get rid of the lambda too, if you like:
list(map(print,primes))
But, at that point you are better off with letting print handle it:
print(*primes, sep='\n')
NOTE: I said earlier that '\n'.join would be a good idea. That is only true for a list of str's.
Solution 2 - Python 3.x
This works for me:
>>> from __future__ import print_function
>>> map(lambda x: print(x), primes)
2
3
5
7
17: [None, None, None, None]
Are you using Python 2.x where print is a statement, not a function?
Solution 3 - Python 3.x
Alternatively, you can unpack it by putting * before map(...) like the following
[*map(...)]
or
{*map(...)}
Choose the output you desire, a list or a dictionary.
Solution 4 - Python 3.x
Another reason why you could be seeing this is that you're not evaluating the results of the map function. It returns a generator (an iterable) that evaluates your function lazily and not an actual list.
primes = [2,3,5,7]
map(print, primes) # no output, because it returns a generator
primes = [2,3,5,7]
for i in map(print, primes):
pass # prints 2,3,5,7
Alternately, you can do list(map(print, primes)) which will also force the generator to be evaluated and call the print function on each member of your list.