Python check that key is defined in dictionary

2018-06-09 15:32:18

This question already has an answer here:

Check if a given key already exists in a dictionary 18 answers

Use the in operator:

if b in a:

Demo:

>>> a = {'foo': 1, 'bar': 2}
>>> 'foo' in a
True
>>> 'spam' in a
False

You really want to start reading the Python tutorial, the section on dictionaries covers this very subject.

Its syntax is if key in dict: :

if "b" in a:
    a["b"] += 1
else:
    a["b"] = 1

Now you may want to look at collections.defaultdict and (for the above case) collections.Counter .

a = {'foo': 1, 'bar': 2}
if a.has_key('foo'):
    a['foo']+=1
else:
    a['foo']=1

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