CODEWITHSUNDEEP
python
Emily
Emily

Reputation: 93

Python: return a specific value while keys not defined

I have a dict h, the keys are int numbers:

from collections import defaultdict

h = defaultdict(dict)
h[1]=['chr1','12','20','1']
h[2]=['chr1','15','20','2']
print(h)

defaultdict(<class 'dict'>, {1: ['chr1', '12', '20', '1'], 2: ['chr1', '15', '20', '2']})

it works:

for i in range(1, 3):
    print(h[i][3])

1
2

but it's possible there are keys which were not defined and have no values, in which case, I want h[i][3] returns value 0. e.g. if I run:

for i in range(1, 5):
    print(h[i][3])

although I have used from collections import defaultdict, the result shows:

1
2
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-45-212d01eedb83> in <module>
      1 for i in range(1, 5):
----> 2     print(h[i][3])

KeyError: 3

My question is, how could I make h[i][3] returns 0 when this i is not defined and then the result should be:

1
2
0
0

Upvotes: 0

Views: 47

Answers (3)

Swazy
Swazy

Reputation: 398

You could use h.get(i,[0]*4)[3]. Should do the trick. Although this assumes you won't index higher than 3. If you index higher you can return a longer array of zeros within the get method.

Upvotes: 1

Gabio
Gabio

Reputation: 9504

The problem is that your values in the dictionary are lists.

So for h[i] defaultdict might help you if i doesn't exist but for the inner access, it can't help since there is no defaultlist which will return something if there is an empty list.

The best you can do is:

h = defaultdict(list)
h[1]=['chr1','12','20','1']
h[2]=['chr1','15','20','2']
for i in range(1, 5):
    print(h[i][3] if h.get(i) and len(h.get(i))>=4 else 0) # checks also that there is at least 4 elements in the list

Upvotes: 1

Sri
Sri

Reputation: 2328

Use a try except.

try:
    for i in range(1, 5):
    print(h[i][3])
except KeyError as e:
    print('Key error - %s' % str(e))
    print(0)

Upvotes: 1

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