searching a namedtuple like a dictionary

Question

to conserve memory & avoid redundant DB storage (yes possibly pre-optimizing), I'm using namedtuple instead of dictionary.

But I need to search the collection of recs and my dictionary approach is:

import operator
def query(D,key,val, keynotfound=None):
    '''
    D:  a list of dictionaries  (but I want it to be namedtuples)
    key:  the key to query
    val:  the value to search for
    keynotfound:  value if key is not found

    Returns elements in D such that operator(D.get(key,None), val) is true
    '''
    op = operator.eq
    def try_op(f,x,y):
        try:
            return f(x,y)
        except Exception, exc:
            return False

    return (x for x in D if try_op(op, x.get(key,keynotfound),val))

not working on namedtuple Any tips on how to subclass namedtuple to make it searchable like a dict? And not every instance will contain the same key/fields as the query-key so I need to skip that row rather than throw a key/attr error..

I'd like this query function to work for both data-types, so rather than change get to getattr, I believe I'll subclass namedtuple and add a "get" method that calls getattr so the interface remains the same......any problems with that?? — Dewey, Feb 28 '15 at 21:27

score 16 · Accepted Answer · answered Feb 28 '15 at 20:38

I think you can use getattr to see if the field exists and either raise an exception or return a default value if it doesn't.

For example, based on the namedtuple documentation:

from collections import namedtuple
Point = namedtuple('Point', ['x', 'y'])

# An instance of the namedtuple
p = Point(1, 2)

In [1]: getattr(p, "x")
Out[1]: 1

In [2]: getattr(p, "z")
...
AttributeError: 'Point' object has no attribute 'z'

In [3]: getattr(f, "z", None)
Out[3]: None

Juergen · Answer 2 · 2015-03-01T00:03:27.523

1

Try this:

return (x for x in D if try_op(op, getattr(x,key,keynotfound),val))

getattr works similar for attributes as get for dictionary elements.

edited Mar 01 '15 at 00:03

answered Feb 28 '15 at 20:40

Juergen

12,378
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score 1 · Answer 3 · answered Mar 01 '15 at 02:33

1

The best solution is to call vars(p), assuming p is your namedtuple instance. This gives a collections.OrderedDict that you can use like a normal dictionary.

answered Mar 01 '15 at 02:33

Peter Shinners

3,686
24
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2

No longer works as of 3.4, as namedtuple no longer implements `__dict__`. namedtuple's `_asdict` method should be used instead. – TakingItCasual Oct 09 '18 at 11:35

searching a namedtuple like a dictionary

3 Answers3