Create a list from multiple attributes

Question

Let's say I have a list of dicts or objects, which effectively looks like this:

[
    {'score': 5, 'tally': 6},
    {'score': 1, 'tally': None},
    {'score': None, 'tally': None},
]

What would be a Pythonic and concise way of creating a list of all ‘score’s and ‘tally’s that are not None? so the result would the following:

[5, 6, 1 ]

Óscar López · Accepted Answer · 2013-07-18 15:40:36Z

4

Try this concise solution, using list comprehensions:

lst = [{'score': 5, 'tally': 6},
       {'score': 1, 'tally': None},
       {'score': None, 'tally': None}]

[v for m in lst for v in m.values() if v is not None]
=> [6, 5, 1]

edited Jul 18, 2013 at 15:40

answered Jul 18, 2013 at 15:00

Óscar López

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4 Comments

Matt Over a year ago

This is really nice, thank you! do you know a similar method if the elements in the list aren't dicts? i.e. score and tally would be attributes on an object.

Óscar López Over a year ago

It'd be similar, because the attributes in an object are stored in the __dict__ attribute of the object

brechin Over a year ago

Note that this particular solution won't report if values are 0 or empty strings, etc. Other "falsy" values that aren't None. To find those as well, change the list comprehension to: [v for m in lst for v in m.values() if v is not None]

Óscar López Over a year ago

@brechin you're right, better to play it safe. I updated my answer, thanks!

inspectorG4dget · Accepted Answer · 2013-07-18 14:57:47Z

1

list(i for i in 
     itertools.chain.from_iterable(
       itertools.izip_longest(
         (d['score'] for d in listOfDicts if d['score'] is not None), 
         (d['tally'] for d in listOfDicts if d['tally'] is not None)
     )) if i is not None)

>>> import itertools
>>> listOfDicts = [
...     {'score': 5, 'tally': 6},
...     {'score': 1, 'tally': None},
...     {'score': None, 'tally': None},
... ]
>>> list(i for i in itertools.chain.from_iterable(itertools.izip_longest((d['sco
re'] for d in listOfDicts if d['score'] is not None), (d['tally'] for d in listO
fDicts if d['tally'] is not None))) if i is not None)
[5, 6, 1]

answered Jul 18, 2013 at 14:57

inspectorG4dget

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3 Comments

Matt Over a year ago

Thanks, I never knew about izip_longest. This is similar to how my solution ended up, I just had the feeling I was missing out on a one line list comprehension.

inspectorG4dget Over a year ago

Yeah, izip_longest comes in handy a lot. Check this out

inspectorG4dget Over a year ago

Happy to help! As a side note, it's awesomely refreshing to be addressed by my real name. Usually, everyone just refers to everyone else by their usernames.

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