Implementing-cryptography-using-python

Chapter 1 ■ Introduction to Cryptography and Python 25
Additionally, Python list objects can also use the index(), count(), remove(),
reverse(), and sort() methods as shown here:
>>> li = ['a', 'b', 'c', 'b']
>>> li.index('b') # index of first occurrence
1
>>> li.count('b') # number of occurrences
2
>>> li.remove('b') # remove first occurrence
>>> li
['a', 'c', 'b']
>>> li = [5, 2, 6, 8]
>>> li.reverse() # reverse the list *in place*
>>> li
[8, 6, 2, 5]
>>> li.sort() # sort the list *in place*
>>> li
[2, 5, 6, 8]
>>> li.sort(some_function) # sort in place using user-defined comparison
One thing to keep in mind when you are debating between using tuples
versus lists is that the list objects are slower but are more powerful than tuples.
Lists can be modified and have many operations that can be used on them. You
can convert between tuples and lists by using the list() and tuple() functions,
as shown here:
li = list(tu)
tu = tuple(li)
Dictionaries provide a way to store a mapping between a set of keys and a set
of values. The keys can be any immutable type, whereas the values can be any
type. A single dictionary can store a range of different types and allow you to
define, modify, view, look up, and delete a key-value pair within the dictionary.
Here is an example of a dictionary:
>>> d = {'user':'bozo', 'pswd':1234}
>>> d['user']
'bozo'
>>> d['pswd']
1234
>>> d['bozo']
Traceback (innermost last):
File '<interactive input>' line 1, in ?
KeyError: bozo
>>> d = {'user':'bozo', 'pswd':1234}