In this chapter, we will cover the following recipes:

• Why Python is a great option for security scripting
• Python 3 language basics and differences

Before going deep into the uses of Python and its modules in security scripting, we need to have an idea about the language basics and different versions. Also, it would be great if we could have an idea of why Python is an awesome option for security scripting.

In the wake of big security attacks and breaches, security/penetration testing is gaining momentum in the quality field. As a popular language in the programming area, it is evident from the tools, books, and scripts published in the last couple of years that Python has become the favorite scripting language for security researchers and hackers.

Even though network and application security is inundated with many tools for automated and semi-automated tests, it may not always guarantee success. Improvisation of tools and scripts is the key to pen-testing, and there will always be some tasks that demand to be automated or to be fulfilled in another way. Becoming a successful real-world penetration tester involves a lot of custom scripting and programming tasks.

These are the main reasons for Python's popularity in security scripting and programming.

Python programs can be compiled in any situation where they can be used as compiled and not required frequent changes. This will make Python programs run much faster and provide a better opportunity to remove vulnerabilities and bugs. Also, interpreted programs run much slower than compiled programs, and are more prone to vulnerabilities and attacks.

Python code uses no compiler and can run on just about any device that runs the Python shell. Also, it shares a couple of other resemblances to scripting languages over programming languages. So, Python can be used to perform the functions of a scripting language.

The syntax and indented layout of Python makes it easy to figure out what is happening in a program during the review. The indentation also makes the program more readable and helps make the collaborative programming easier.

Learning a new programming language is always a rigorous task. But Python was designed in such a way that it should be easily learned by even a novice programmer. Python's growing acceptance with the programmers is mainly due to its easiness to learn and its design philosophy highlights code readability that will help the beginner developers to learn many things by reading the code itself. Also, Python's read evaluate print loop (REPL) provides the developer a chance to play around with code and experiment with it. The standard Python library maintains a lot of functionalities with which we can execute complex functionalities with ease.

Once you have learned Python, you can leverage the platform backed with a large number of libraries. The Python Package Index (PyPI), is a repository of more than 85,000 reusable Python modules and scripts that you can use in your scripts. Python is the best language to learn as a security researcher, because of the availability of its large number of reverse engineering and exploitation libraries.

Python works on Linux, Microsoft Windows, macOS X, and many other operating systems and devices. A Python program written on a macOS X computer will run on a Linux system and vice versa. Also, Python programs can run on Microsoft Windows computers, as long as the machine has Python interpreter installed.

Python 3.0 was first released in 2008. Even though Python 3 supposed to be backward incompatible with other old version, many of its features are backported to support older versions. It is better to have an idea of Python versions and its differences for better understanding of our recipes.

If you are new to Python, you might be confused about the different versions that are available. Before looking into the further details, let's have a look at the most recent major releases of Python and the key differences between Python 2 and Python 3.

These are the major Python versions available.

Published in late 2000, it has many more programmatic features including a cycle-detecting garbage collector that helps to automate memory management. The increased unicode support that helps to standardize characters, and list comprehensions that help to create a list based on existing lists are other features. In Python version 2.2, the types and classes are consolidated into one hierarchy.

Python 3 was released in late 2008, to update and fix the built-in design flaws of the prior versions of Python. The main focus of Python 3 development was to clean up the code base and reduce redundancy.

In the beginning, the adoption of Python 3 was a very slow process due to its backward incompatibility with Python 2. Moreover, many package libraries were only available for Python 2. Later, there was an increased adoption for Python 3 as the development team announced that there will be an end of life for Python 2 support and more libraries have been ported or migrated to Python 3.

Python 2.7 was published in 2010 and was planned as the last release for 2.x versions. Its intention was to make it easier for Python 2.x users to port their features and libraries over to Python 3 by providing compatibility between the two, which included a unit test to support test automation, argparse for parsing command-line options, and more convenient classes in collections.

Here are some main differences between Python 2.x and Python 3:

• Print: In Python 2, print is a statement. So, there is no need to wrap the text in parentheses for printing. But in Python 3 print is a function. So, you have to pass the string you need to print to the function in parentheses.
• Integer division: Python 2 considers numbers without any digits after the decimal point as integers, which may lead to some unexpected results during division.
• List comprehension loop variables leak: In Python 2, giving the variable that is iterated over in a list comprehension leaks the variable into surrounding scope, this list comprehension loop variable leak bug has been fixed in Python 3.
• Unicode strings: Python 2 requires you to mark the unicode string explicitly with the u prefix. But, Python 3 stores strings as unicode by default.
• Raising exceptions: Python 3 requires different syntax for raising exceptions.

The progression from Python 2.x to Python 3.x is happening slowly, but it is underway. It is good to be mindful that there are material differences between Python 2.x and Python 3 as you may need to deal with code that is written in the version with which you are less familiar.