If we try to fetch the value of a key that does not exist, we get an exception.

examples/dictionary/no_such_key.py
from __future__ import print_function

user = {
    'fname': 'Foo',
    'lname': 'Bar',
}

print(user['fname'])
print(user['email'])

# Foo
# Traceback (most recent call last):
#   File "examples/dictionary/no_such_keys.py", line 9, in <module>
#     print user['email']
# KeyError: 'email'