Implementing-cryptography-using-python

26 Chapter 1 ■ Introduction to Cryptography and Python
>>> d['user'] = 'clown'
>>> d
{'user':'clown', 'pswd':1234}
>>> d['id'] = 45
>>> d
{'user':'clown', 'id':45, 'pswd':1234}
>>> d = {'user':'bozo', 'p':1234, 'i':34}
>>> del d['user'] # Remove one.
>>> d
{'p':1234, 'i':34}
>>> d.clear() # Remove all.
>>> d
{}
>>> d = {'user':'bozo', 'p':1234, 'i':34}
>>> d.keys() # List of keys.
['user', 'p', 'i']
>>> d.values() # List of values.
['bozo', 1234, 34]
>>> d.items() # List of item tuples.
[('user','bozo'), ('p',1234), ('i',34)]
Introducing Python Functions
Introducing Custom Functions
Now that you understand strings, let’s examine reusable code. In Python, you create
a new function and assign it a name by using the def keyword. All functions
in Python return results to the calling statement. Arguments are passed by
assignment, and arguments and return types are not declared. When you pass
arguments to a function, the values are assigned to locally scoped names. The
assignment to argument names will not affect the caller since they are passed
by assignment and not by reference. You will, however, affect the caller if you
change a mutable argument.
Create a new file in your editor of choice and type the following:
def myEnc(plaintext, key):
return "ciphertext"
Save the file as MyFunctions.py. In the command line, type MyFunctions.py.
You should notice that nothing happens. Now type the following:
myEnc('hello','secret key')
The output should be ciphertext.
The script you created is an example of a function. The def keyword is used
to define the function; as you might have guessed, myEnc is the name of the
function. It takes two parameters or inputs and returns an output. We use
functions to build logic we intend to use multiple times. The benefit of using