Getting a map() to return a list in Python 3.x

Question

I'm trying to map a list into hex, and then use the list elsewhere. In python 2.6, this was easy:

A: Python 2.6:

>>> map(chr, [66, 53, 0, 94])
['B', '5', '\x00', '^']

However, in Python 3.1, the above returns a map object.

B: Python 3.1:

>>> map(chr, [66, 53, 0, 94])
<map object at 0x00AF5570>

How do I retrieve the mapped list (as in A above) on Python 3.x?

Alternatively, is there a better way of doing this? My initial list object has around 45 items and id like to convert them to hex.

Answer 1

I'm not familiar with Python 3.1, but will this work?

[chr(x) for x in [66, 53, 0, 94]]

Answer 2

list(map(chr, [66, 53, 0, 94]))

map(func, *iterables) --> map object Make an iterator that computes the function using arguments from each of the iterables. Stops when the shortest iterable is exhausted.

"Make an iterator"

means it will return an iterator.

"that computes the function using arguments from each of the iterables"

means that the next() function of the iterator will take one value of each iterables and pass each of them to one positional parameter of the function.

So you get an iterator from the map() funtion and jsut pass it to the list() builtin function or use list comprehensions.

Answer 3

List-returning map function has the advantage of saving typing, especially during interactive sessions. You can define lmap function (on the analogy of python2's imap) that returns list:

lmap = lambda func, *iterable: list(map(func, *iterable))

Then calling lmap instead of map will do the job: lmap(str, x) is shorter by 5 characters (30% in this case) than list(map(str, x)) and is certainly shorter than [str(v) for v in x]. You may create similar functions for filter too.

There was a comment to the original question:

I would suggest a rename to Getting map() to return a list in Python 3.* as it applies to all Python3 versions. Is there a way to do this? – meawoppl Jan 24 at 17:58

It is possible to do that, but it is a very bad idea. Just for fun, here's how you may (but should not) do it:

__global_map = map #keep reference to the original map
lmap = lambda func, *iterable: list(__global_map(func, *iterable)) # using "map" here will cause infinite recursion
map = lmap
x = [1, 2, 3]
map(str, x) #test
map = __global_map #restore the original map and don't do that again
map(str, x) #iterator