Iterating over dictionaries using 'for' loops

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I am a bit puzzled by the following code:

d = {'x': 1, 'y': 2, 'z': 3} 
for key in d:
    print key, 'corresponds to', d[key]

What I don't understand is the key portion. How does Python recognize that it needs only to read the key from the dictionary? Is key a special word in Python? Or is it simply a variable?

Oct 8, 2018 in Python by ana1504.k
• 5,910 points
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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 2.x:

for key, value in d.iteritems():
For Python 3.x:

for key, value in d.items():
answered Oct 8, 2018 by SDeb
• 9,380 points

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