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..

Answer 1

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

Answer 2

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.

Answer 3

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.