operator.setitem problem in python 3

I have a problem when using operator.setitem in python 3.

When I use the code below and run it in python 3.1.

people=(('fred','sam','jane','bett开发者_StackOverflowy'),(1,2,3,4))
p_dict = {}
map(operator.setitem, [p_dict]*len(people[0]), people[0],people[1])
print (p_dict)

>>> {}

That just prints out a empty dictionary {}.

But I use the same code to run in python 2.6. It prints out {'jane': 3, 'betty': 4, 'sam': 2, 'fred': 1} . This is the result I want.

So, can anyone tell me what's the problem when I run this code in python 3? Thanks in advance.

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That's a very unpythonesque way to do it. This is much better (and more efficient):

people = (('fred','sam','jane','betty'), (1,2,3,4))
p_dict = dict(zip(*people))

Works on 2.x and 3.x.

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The problem is that the map() is never 'executed'. In Python 3, map just returns an iterator - the individual elements are only computed when they are needed. To work around that, you might write

list(map(operator.setitem, [p_dict]*len(people[0]), people[0],people[1]))

However, I agree with everybody else that you shouldn't be using map in the first place - as you don't really need to result of the map application.

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In Python 3, the result of map is lazy which can give you headache when debugging stuff that worked flawlessly in older versions of Python. In other words, it is a generator, so you have to consume it in order to set the items in your dictionary.

You should rather do this with a for loop in this case:

people=(('fred','sam','jane','betty'),(1,2,3,4))
p_dict = {}
for key, value in zip(*people):
    p_dict[key] = value
# Now p_dict is {'jane': 3, 'betty': 4, 'sam': 2, 'fred': 1}

or with a simple dict constructor: dict(zip(*people)).