Check if in dict or try/except which has better performance in python?

Question

I have a few dictionaries containing similar data.

Most queries would be resolved in a single search of one dictionary.

So is it better performance wise to leave out preliminary checks for existence of a key in a dict and have a try at the next dict in an except clause catching key error?

Or maybe something like

# d1, d2, d3 = bunch of dictionaries

value = d1.get(key, d2.get(key, d3.get(key, 0)))

?

Answer 1

It seems in almost all cases, using get would be faster. Here is my test run using try..except and get

>>> def foo1(n):
    spam = dict(zip(range(-99,100,n),[1]*200))
    s = 0
    for e in range(1,100):
        try:
            s += spam[e]
        except KeyError:
            try:
                s += spam[-e]
            except KeyError:
                s += 0
    return s

>>> def foo2(n):
    spam = dict(zip(range(-99,100,n),[1]*200))
    s = 0
    for e in range(1,100):
        s += spam.get(e, spam.get(-e,0))
    return s


>>> for i in range(1,201,10):
    res1 =  timeit.timeit('foo1({})'.format(i), setup = "from __main__ import foo1", number=1000)
    res2 =  timeit.timeit('foo2({})'.format(i), setup = "from __main__ import foo2", number=1000)
    print "{:^5}{:10.5}{:10.5}{:^10}{:^10}".format(i,res1,res2,foo1(i),foo2(i))


  1    0.075102  0.082862    99        99    
 11     0.25096  0.054272    9         9     
 21      0.2885  0.051398    10        10    
 31     0.26211  0.060171    7         7     
 41     0.26653  0.053595    5         5     
 51      0.2609  0.052511    4         4     
 61      0.2686  0.052792    4         4     
 71     0.26645  0.049901    3         3     
 81     0.26351  0.051275    3         3     
 91     0.26939  0.051192    3         3     
 101      0.264  0.049924    2         2     
 111     0.2648  0.049875    2         2     
 121    0.26644  0.049151    2         2     
 131    0.26417  0.048806    2         2     
 141    0.26418  0.050543    2         2     
 151    0.26585  0.049787    2         2     
 161    0.26663  0.051136    2         2     
 171    0.26549  0.048601    2         2     
 181    0.26425  0.050964    2         2     
 191     0.2648  0.048734    2         2     
>>>

Answer 2

Depends on the keys in the dictionaries.

If you predict with confidence that it is more common for keys to be missing use then use get.

If you predict with confidence that it is more common for keys to be there use try except.