Python create tuples using function returning multiple values

Question

I have a list of tuples, and I need to add more information to each tuple. The list looks something like this:

[(name1, value1), (name2, value2), (name1, value3), ...]

I have a function to get the extra information for each tuple, but I need the new tuples to be flat and I can't think of a good way to do that in a list comprehension. I would love to be able to do something like this:

new_list = [(name, value, *extra_info(name)) for name, value in old_list]

or

new_list = [list(name, value, *extra_info(name)) for name, value in old_list]

Unfortunately the first one is bad syntax, and the second one doesn't work because list only takes in one argument. Is there a way to unpack the tuple returned by extra_info in a list comprehension? Failing that, what would be the most Pythonic way to tackle this problem?

To be clear, I want to end up with a list that looks like this:

[(name1, value1, extra1, extra2), (name2, value2, extra3, extra4), (name1, value3, extra1, extra2), ...]

(name, value) + extra_info(name)? Assuming extra_info returns a tuple? — g.d.d.c
– g.d.d.c, Commented Sep 30, 2014 at 22:27
@g.d.d.c Yes, extra_info returns multiple values, so they get packed into a tuple. — Rob Watts
– Rob Watts, Commented Sep 30, 2014 at 22:34

iurisilvio · Accepted Answer · 2014-09-30 22:36:10Z

2

You have to sum lists and convert it to a tuple.

new_list = [(name, value) + extra_info(name) for name, value in old_list]

edited Sep 30, 2014 at 22:36

answered Sep 30, 2014 at 22:28

iurisilvio

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1 Comment

Rob Watts Over a year ago

Multiple values get returned as a tuple, and name and value are already in a tuple so I can just add the tuples. This will work perfectly for me!

Tony Suffolk 66 · Accepted Answer · 2014-09-30 22:35:16Z

2

try :

  new_list = [(name, value) + extra_info(name) for name, value in old_list]

no need for converting tuples to lists ...

answered Sep 30, 2014 at 22:35

Tony Suffolk 66

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Comments

Rob Watts · Accepted Answer · 2014-09-30 22:58:10Z

0

Something I came up with while thinking about this was to use a lambda echo function to pack the new tuples:

packer = lambda *x: x
new_list = [packer(name, value, *extra_info(name)) for name, value in old_list]

answered Sep 30, 2014 at 22:58

Rob Watts

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