CODEWITHSUNDEEP
pythonpython-3.xset
Craig
Craig

Reputation: 843

1 liner 'pythonic' code that returns a set rather than a list

I would like to do the following code, except in a neat 1-liner: 

terms_set = set([])
for term in terms: 
    if index.has_key(term): 
        terms_set.add(index[term])

Is it possible to do? Must return a set.

Upvotes: 4

Views: 98

Answers (5)

SingleNegationElimination
SingleNegationElimination

Reputation: 156228

So it looks like you want term_set to contain all of the values in index (some dict), so long as its' key is also mentioned in terms (some iterable). regarding both as sets, that's intersection, which is roughly, for the keys at least, set(terms) & set(index), but that generates two sets, and we're actually interested in neither (we want values, not keys). We can elide one of them with set(terms).intersection(index) (or visa versa, depending on which one is larger (we want the smaller on the left).

We can use our good friend map to get the values.

how about this?

term_set = map(index.get, set(terms).intersection(index))

or even:

term_set = map(index.get, index.keys() & terms)

(in python2.7, you would need index.viewkeys())

Hmm... thinking about it, dict.get can return a default value (ie None), which we could strip out after-the fact (if it occured)

term_set = set(map(index.get, terms))
term_set.discard(None)

which construts NO intermediate collections (assuming python3, otherwise map should be itertools.imap)

Although if None can occur as a value in index, you'd end up having to do something tedious like:

sentinel = object()
term_set = {index.get(term, sentinel) for term in terms} - {sentinel}

which is not at all better than the accepted answer.

Upvotes: 2

lvc
lvc

Reputation: 35089

You can use a set comprehension:

terms_set = {index[term] for term in terms if term in index}

Note that key in dict is preferred over dict.has_key, which was deprecated in Python 2 and is not available in Python 3.

Upvotes: 7

levi
levi

Reputation: 22697

terms_set = set([index[term] for term in terms if index.has_key(term)])

Upvotes: 0

Travis Griggs
Travis Griggs

Reputation: 22252

terms_set = set(index[term] for term in terms if index.has_key(term))

Upvotes: 2

georg
georg

Reputation: 214979

This?

set(index[t] for t in terms if t in index)

Note that has_key is deprecated, use key in dict instead.

Upvotes: 1

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