Implementing-cryptography-using-python

Chapter 1 ■ Introduction to Cryptography and Python 11
that in Python, variable names are case sensitive, so age and Age represent two
different variables. This overview shows the use of variables with numbers; we
will examine the use of variables and strings next.
Using Strings
Strings allow you to use text in programming languages. In cryptography, you
use strings a great deal to convert plaintext to ciphertext and back. These values
are stored in variables much like the numeric examples used in the preceding
section. Strings in Python are stored using the single quote (‘) or double quote
(“); it does not matter which quote you use as long as they are matching. To see
an example, type the following into the shell:
>>> name = 'John'
>>> name
'John'
The single quotes are not part of the string value. Python only evaluates the
data between the quotes. If you wanted to set a variable to an empty string, you
would use the following:
>>> name = ''
In Python, you can concatenate multiple strings together by using the plus
(+) operator. See the following example:
>>> first = 'John'
>>> last = 'Doe'
>>> name = first + last
>>> name
'JohnDoe'
Notice that the strings concatenate exactly the way they store values; if you
need a word separation, plan for the use of spaces.
Introducing Operators
You have now seen the + operator used in both numeric and string variables.
Other operators can be broken down into the following categories: arithmetic,
comparison, logical, assignment, bitwise, membership, and identity.
Understanding Arithmetic Operators
Arithmetic operators perform mathematical calculations (see Table 1.1).