Python dict.get('key') versus dict['key'] [duplicate]

Question

Why does this throw a KeyError:

d = dict() d['xyz'] 

But this does not?

d = dict() d.get('xyz') 

I'm also curious if descriptors play a role here.

Answer 1

This is simply how the get() method is defined.

From the Python docs:

Return the value for key if key is in the dictionary, else default. If default is not given, it defaults to None, so that this method never raises a KeyError.

The default "not-found" return value is None. You can return any other default value.

d = dict() d.get('xyz', 42)  # returns 42 

Answer 2

Accessing by brackets does not have a default but the get method does and the default is None. From the docs for get (via a = dict(); help(a.get))

Help on built-in function get:  get(...)     D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None.