python for loop expression of iterator

Question

I have a for loop in which I use the iterator always in the same manner, like this

for dict in mylist:
    var = dict['prop']
    var2 = f( dict['prop'] )
    ...

This is clumsy. The only alternatives I can think of:

local variable
wrapping the mylist in a list comprehension. But that seems overkill and is probably inefficient

Any better way?

I don't see any problems with that, although I'd write it as var, var2 = dict['prop'], f(dict['prop']) — vaultah, 1 hour ago
To be honest, I am not seeing the clumsiness (except the unnecessary second lookup of dict['prop']). Perhaps show us more of your code? — NPE, 1 hour ago
for dict_prop=dict['prop'] in mylist: ... would seem more natural for me. Just looking if I missed some python feature — Basti, 1 hour ago

vaultah · Answer 1 · 2014-10-04 08:15:43Z

I'm not sure if this is prettier but you can construct a generator in for loop definition:

>>> a = [{'prop': 1}, {'prop': 2}]
>>> for x in (x['prop'] for x in a):
...     print(x)
... 
1
2

Or use operator.itemgetter and map:

>>> from operator import itemgetter
>>> for x in map(itemgetter('prop'), a):
...     print(x)
... 
1
2

This won't make extra dictionary lookups and starting from Python 3 map is as efficient as a generator.

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