174 http://inventwithpython.com/hacking

Email questions to the author: [email protected]

The not in operator works with dictionary values as well.

Using for Loops with Dictionaries

You can also iterate over the keys in a dictionary with for loops, just like you can iterate over
the items in a list. Try typing the following into the interactive shell:

spam = {'name':'Al', 'age':99}
for k in spam:
... print(k)
... print(spam[k])
... print('==========')

age
99

name
Al

Practice Exercises, Chapter 12, Set C

Practice exercises can be found at http://invpy.com/hackingpractice12C.

The Difference Between Dictionaries and Lists

Dictionaries are like lists in many ways, but there are a few important differences:

1. Dictionary items are not in any order. There is no “first” or “last” item in a dictionary like
   there is in a list.


2. Dictionaries do not have concatenation with the + operator. If you want to add a new
   item, you can just use indexing with a new key. For example, foo['a new key'] =
   'a string'


3. Lists only have integer index values that range from 0 to the length of the list minus one.
   But dictionaries can have any key. If you have a dictionary stored in a variable spam,
   then you can store a value in spam[3] without needing values for spam[0],
   spam[1], or spam[2] first.