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pythontuplesgeneratoryield

python function yields tuple and only one element is wanted

I have a function 

def f():
    # whatever
    yield (a,b)

Now I would like to collect all the a but not b. Also I want the result aa to be a list instead of iterator. Right now I use

aa, _ = zip(*f())

Is this the best one can do in terms of space/time efficiency?

Solution

  • zip(*seq) has to ingest the whole generator, before it can output the columns. This is not efficient.

    Just stick to a list comprehension. You could use tuple assignment:

    aa = [a for a, _ in f()]

    or use indexing:

    aa = [tup[0] for tup in f()]

    If you don't have to have all values available for random access or other operations that must have a list, you can use a generator expression to maintain the memory efficiency:

    aa = (a for a, _ in f())