Efficient way to remove keys with empty strings from a dict

Question

I have a dict and would like to remove all the keys for which there are empty value strings.

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Answer 1

Some benchmarking:

1. List comprehension recreate dict

In [7]: %%timeit dic = {str(i):i for i in xrange(10)}; dic['10'] = None; dic['5'] = None
   ...: dic = {k: v for k, v in dic.items() if v is not None} 
   1000000 loops, best of 7: 375 ns per loop

2. List comprehension recreate dict using dict()

In [8]: %%timeit dic = {str(i):i for i in xrange(10)}; dic['10'] = None; dic['5'] = None
   ...: dic = dict((k, v) for k, v in dic.items() if v is not None)
1000000 loops, best of 7: 681 ns per loop

3. Loop and delete key if v is None

In [10]: %%timeit dic = {str(i):i for i in xrange(10)}; dic['10'] = None; dic['5'] = None
    ...: for k, v in dic.items():
    ...:   if v is None:
    ...:     del dic[k]
    ...: 
10000000 loops, best of 7: 160 ns per loop

so loop and delete is the fastest at 160ns, list comprehension is half as slow at ~375ns and with a call to dict() is half as slow again ~680ns.

Wrapping 3 into a function brings it back down again to about 275ns. Also for me PyPy was about twice as fast as neet python.