Python check that key is defined in dictionary [duplicate]

Question

How to check that the key is defined in dictionary in python?

a={} ... if 'a contains key b':   a[b] = a[b]+1 else   a[b]=1 

Answer 1

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.

Answer 2

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.