key is just a variable name.
for key in d:
will simply loop over the keys in the dictionary, rather than the keys and values. To loop over both key and value you can use the following:
For Python 3.x:
for key, value in d.items():
For Python 2.x:
for key, value in d.iteritems():
To test for yourself, change the word
In Python 3.x,
iteritems() was replaced with simply
items(), which returns a set-like view backed by the dict, like
iteritems() but even better.
This is also available in 2.7 as
items() will work for both 2 and 3, but in 2 it will return a list of the dictionary’s
(key, value) pairs, which will not reflect changes to the dict that happen after the
items() call. If you want the 2.x behavior in 3.x, you can call