Python call class with inputs from list

Question

I have a class called Interval for which I want to create multiple interval objects from a list of intervals. How do I do it with map ?

class Interval(object):
    def __init__(self, s=0, e=0):
        self.start = s
        self.end = e

intervals = [[1,2],[3,5],[6,7],[8,10],[12,16]]

I tried to do:

objs = map(Interval, intervals)

But this sends the full interval as the first parameter rather than the inputs to the class individually.

@AlanLeuthard: it works, but then s will get a list as input, and e will be 0 for all cases... — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jun 7, 2017 at 23:01

willeM_ Van Onsem · Accepted Answer · 2017-06-07 23:01:12Z

2

You can use starmap from itertools:

from itertools import starmap

objs = starmap(Interval,intervals)

Mind that starmap works lazily (like map in Python-3.x) and that you will need to materialize it, for instance using list(..):

>>> list(objs)
[<__main__.Interval object at 0x7efbf7e82358>, <__main__.Interval object at 0x7efbf7e82390>, <__main__.Interval object at 0x7efbf7e823c8>, <__main__.Interval object at 0x7efbf7e82400>, <__main__.Interval object at 0x7efbf7e82438>]

If you do not want to use the itertools library, an equivalent is:

objs = map(lambda x: Interval(*x),intervals)

As far as I know, that's why they call it starmap: because of the asterisk if you would use a lambda expression.

edited Jun 7, 2017 at 23:01

answered Jun 7, 2017 at 22:55

willeM_ Van Onsem

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2 Comments

developer_hatch Over a year ago

Are you everywhere at this time of the night? hahaha, and also better answer... I must admit

Pritam Over a year ago

Ah! starmap, this is what I was looking for. Thanks!

Alan Leuthard · Accepted Answer · 2017-06-07 23:07:30Z

2

This worked for me.

>>> objs = []
>>> for interval in intervals:
...     objs.append(Interval(*interval))
... 
>>> objs
[<__main__.Interval object at 0x013E67D0>, <__main__.Interval object at 0x013E6910>, <__main__.Interval object at 0x013E68F0>, <__main__.Interval object at 0x013E6870>, <__main__.Interval object at 0x013E6950>]
>>> objs[0]
<__main__.Interval object at 0x013E67D0>
>>> objs[0].start
1
>>> objs[0].end
2
>>>

answered Jun 7, 2017 at 23:07

Alan Leuthard

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Comments

developer_hatch · Accepted Answer · 2017-06-07 23:07:29Z

0

Maybe you can try also the old-school way:

class Interval(object):
    def __init__(self, s=0, e=0):
        self.start = s
        self.end = e


def map_intervals(intervals):
        ret = []
        for inter in intervals:
          ret.append(Interval(inter[0],inter[1]))
        return ret
inters = [[1,2],[3,5],[6,7],[8,10],[12,16]]

answered Jun 7, 2017 at 23:07

developer_hatch

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