for key, value in dict.<func>() - how to get? (which func)

[dmitrey]

hi all,
which method should I use to get iterator over (key, value) pairs for
Python dict, Python v 2.6 and above?

Of course I could use

for key in myDict.keys():
value = myDict.values()
# do something with the pair key, value

but searching each time for the value take some cputime that is
serious for the task involved

IIRC in python 2.5 I have something like keyvalues(), but I don't see
something like that in current dir(myDict).

Thank you in advance, D.

 

[Rami Chowdhury]

Hi Dmitrey,

I think what you're looking for is myDict.items(), or myDict.iteritems().

Cheers,
Rami

 

[dmitrey]

Yes, thank you, items() is the correct approach, on the other hand I
have already get rid of the cycle.
Regards, D.

 

[Gary Duzan]

hi all,
which method should I use to get iterator over (key, value) pairs for
Python dict, Python v 2.6 and above?

dict.iteritems()

Gary Duzan
Motorola H&NM

 

[Diez B. Roggisch]

Yes, thank you, items() is the correct approach, on the other hand I
have already get rid of the cycle.

Most certainly items() is *not* the correct approach if you are
concerned so much with performance, because items() first creates a list
of key/value-pairs, where iteritems() will be an effective iterator.

so if you are (IMHO wrongly) concerned about performance of an O(1)
lookup, items() certainly costs more.

And the following program proves it:

import time

d = dict(zip(xrange(100000), xrange(100000)))

start = time.time()
for loops in xrange(100):
for key in d:
value = d[key]

print "lookup: ", time.time() - start

start = time.time()

for loops in xrange(100):
for key, value in d.items():
value = d[key]


print "items: ", time.time() - start

start = time.time()

for loops in xrange(100):
for key, value in d.iteritems():
value = d[key]


print "items: ", time.time() - start


The result on my machine is:

deets$ python /tmp/test.py

lookup: 2.78633999825
items: 7.42830610275
items: 3.69960308075

So actually your condemed approach seems to be the fastest, where the
items() call by far is the slowest approch.

"In the face of ambiguity, refuse the temptation to guess."


Diez