How to create a list of named lists in Python?

Question

I need to create a list of named lists, so that I can iterate over them. This works, but I'm wondering if there isn't a better way.

terms = []; usedfors = []; broaders = []; narrowers = []
termlist = [terms, usedfors, broaders, narrowers]

The reason for doing it this way is that I have a function do_some_list_operation(l) and I want to do something like

for i in termlist:
    do_some_list_operation(i)

rather than

do_some_list_operation(terms)
do_some_list_operation(usedfors)
do_some_list_operation(broaders)
do_some_list_operation(narrowers)

I've been searching for 'how to build list of named lists' to no avail.

What do you mean by a named list? Do you mean a dict perhaps? — msaw328
– msaw328, Commented Dec 23, 2021 at 17:14
Your for loop looks good to me as is at the moment. unless your termlist is strings like termlist = ["terms", "usedfors", "broaders", "narrowers"] — JonSG
– JonSG, Commented Dec 23, 2021 at 17:19
@msaw328 By named lists I mean each name should reflect what's in them, rather than mylist[0], mylist[1], etc. I chose list because they need to be an ordered collection of strings. I'd use dict or OrderedDict for key-value pairs. — RolfBly
– RolfBly, Commented Dec 23, 2021 at 20:21

Jayvee · Accepted Answer · 2021-12-23 18:25:12Z

3

The way you are doing it is fine but be aware that you are creating a list of lists when you defined termlist. If you want to have the name of the lists then termlist should be:

termlist = ["terms","usedfors", "broaders", "narrowers"]

Now if you want to use these strings as list names you can use globals() or locals() e.g.:

terms = [1]; usedfors = [2]; broaders = [3,4,8]; narrowers = [5]
termlist = ["terms","usedfors", "broaders", "narrowers"]

for i in termlist:
    print(sum(locals()[i]))

output:

answered Dec 23, 2021 at 18:25

Jayvee

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JonSG · Accepted Answer · 2021-12-24 16:21:41Z

1

While I like the answer by @jayvee and upvoted it, I think a more conventional answer would be one based on using a dictionary as first suggested by @msaw328.

Starting with our new data structure:

term_data = {
    "terms": [1],
    "usedfors": [2],
    "broaders": [3, 4, 5],
    "narrowers": [6, 7]
}

Perhaps like:

for term in term_data:
    print(f"{term} sums to {sum(term_data[term])}")

or even

for term, term_value in term_data.items():
    print(f"{term} sums to {sum(term_value)}")

Both should give you:

terms sums to 1
usedfors sums to 2
broaders sums to 12
narrowers sums to 13

answered Dec 24, 2021 at 16:21

JonSG

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