get keys and values from a Python dictionary as lists

Question

I have the following output from a code I ran on Python:

T1 =  [{0: 0}, {15: 3}, {19: 1}, {20: 1}, {0: 0}]

I want to extract the keys and values from each object respectively. For T1, I would thus have:

P1 =  [0,15,19,20,0]
D1 = [0, 3, 1,1,0]

What would be the best way to code it?

Thanks in advance,

Answer 1

Sounds like a good case for chain.from_iterable :

>>> from itertools import chain
>>> from operator import methodcaller

>>> T1 =  [{0: 0}, {15: 3}, {19: 1}, {20: 1}, {0: 0}]

>>> list(chain.from_iterable(T1))
[0, 15, 19, 20, 0]

>>> list(chain.from_iterable(map(methodcaller('values'), T1)))
[0, 3, 1, 1, 0]

A dictionary when iterated over yields its keys; chain.from_iterable takes a list of such iterables and yields all their keys in a sequence. To do the same with the values, call values() on each item, for which we map a methodcaller here (equivalent to (i.values() for i in T1) ).

Answer 2

this should work:

T1 = [{0: 0}, {15: 3}, {19: 1}, {20: 1}, {0: 0}]

P1 = [next(iter(dct)) for dct in T1]
D1 = [next(iter(dct.values())) for dct in T1]

you take the first element ( next ) of an iterator over the keys ( iter(dct) ) or an interator over the values ( iter(dct.values() ).

this will not create any unnecessary lists.

or in one go (note: these return tuples not lists ):

P1, D1 = zip(*(next(iter(dct.items())) for dct in T1))

or (using parts of deceze's answer ):

from itertools import chain

P1, D1 = zip(*chain.from_iterable(dct.items() for dct in T1))

Answer 3

UseList Comprehensions :

In [148]: P1 = [list(i.keys())[0] for i in T1]

In [149]: D1 = [list(i.values())[0] for i in T1]

In [150]: P1
Out[150]: [0, 15, 19, 20, 0]

In [151]: D1
Out[151]: [0, 3, 1, 1, 0]