Implementing-cryptography-using-python

Chapter 1 ■ Introduction to Cryptography and Python 27
functions is that if you decide you need to change the script, you can change it
in one place and not have to search for other areas in which you performed the
same logic. This will help in both troubleshooting and code maintenance. We
will be using functions quite a bit throughout this book.
In Python, you can declare some arguments as optional. Examine the following
segment of code, paying attention to the third and fourth arguments:
def func(a, b, c=10, d=100):
! print (a, b, c, d)
>>> func(1,2)
1 2 10 100
>>> func(1,2,3,4)
1,2,3,4
Something to watch out for is that all functions have a return value even if
you do not provide a return line inside the code. Functions that do not provide
a return line will return the special value of None. Note also that, unlike other
languages, Python does not provide a way to overload a method, so you are not
allowed to have two different functions with the same name and a different
list of arguments. Some benefits to functions include that they can be used as
arguments to functions, return values of functions, and be assigned to variables,
and may contain parts of tuples, lists, and other objects.
Downloading Files Using Python
You can download files and content in Python in a number of ways. One of the
preferred ways in Python 3 is to use the requests module. The get method of
the requests module is used to download the file contents in binary format. You
can then use the open method to open a file on your system. Here’s an example
of downloading files using the requests module:
>>> import requests
>>> print('Beginning file download with requests')
>>> url = 'https://raw.githubusercontent.com/noidentity29/
AppliedCryptoPython/master/secret.txt'
>>> r = requests.get(url)
>>>
>>> # Windows Path - C:\Users\ShannonBray\Downloads\
>>> with open('/Users/ShannonBray/Downloads/secrets.txt', 'wb') as f:
>>> f.write(r.content)
>>>
>>> # Retrieve HTTP meta-data
>>> print(r.status_code)
>>> print(r.headers['content-type'])
>>> print(r.encoding)
>>>