Chapter 1, Our Espionage Toolkit, exposes the basics of installing and using Python. We'll write scripts to help agents work with foreign currency conversions and learn how an agent can recover a lost password from a ZIP archive.

Chapter 2, Acquiring Intelligence Data, shows how we can use Python to extract information from various kinds of file servers. Agents will learn how to work with different Internet protocols and use Representational State Transfer (REST) to interact with web services. This will include techniques to work with cyptocurrencies, such as bitcoins.

Chapter 3, Encoding Secret Messages with Steganography, shows how we can add the Pillow toolset to work with images. An agent with Pillow can create thumbnails and convert, crop, and enhance images. We'll also explore some steganography algorithms to bury our messages in an image file.

Chapter 4, Drops, Hideouts, Meetups, and Lairs, provides a closer look at geocoding and geolocation. This includes the use of web services to convert an address into a latitude and longitude. We'll also learn how to convert a latitude and longitude back into an address. We'll take a look at the haversine formula to get the correct distance between locations. We'll also look at some of the ways in which geographic locations can be represented for tidy storage and communication.

Chapter 5, A Spymaster's More Sensitive Analyses, shows how we can use Python for a basic data analysis. A good agent doesn't just spout facts and figures; a good agent does enough analysis to confirm that the data is realistic. Being able to examine the correlation between datasets is what creates a valuable intelligence asset.

A secret agent needs a computer that they have administrative privileges over. We'll be installing additional software. Without the administrative password, they may have trouble installing Python 3, Pillow, or BeautifulSoup.

For agents using Windows, the packages we're looking at adding come prebuilt.

For agents using Linux, the developer tools are required. Linux has a complete suite of developer tools that are common. The Gnu C Compiler (GCC) is the backbone of these tools.

For agents using Mac OS X, the developer tool, Xcode (https://developer.apple.com/xcode/), is required. We'll also need to install a tool called homebrew (http://brew.sh) to help us add the Linux packages to Mac OS X.

Python 3 is available from the Python download page at https://www.python.org/download.

We'll download and install several things besides Python 3.3:

From this, we'll see how extensible Python is. Almost anything an agent might need may already be written and available through the Python Package Index (PyPi), which can be downloaded from https://pypi.python.org/pypi.

This book is for secret agents who don't know much Python, but are comfortable installing new software and are ready to do some clever programming in Python. An agent who has never done any programming before might find some of this a bit advanced; a beginner's tutorial that covers the basics of Python may be helpful.

We'll expect that an agent using this book is comfortable with simple math. This involves the multiplication and division of currency conversions. It also includes polynomials, simple trigonometry, and a few statistical formulae.

We also expect the secret agents using this book to be doing their own investigations. The book's examples are designed to get the agent started down the road with developing interesting, useful applications. Each agent will have to explore further afield on their own.

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text, package names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "The size_list variable is a sequence of eight-tuples built from the bytes of the encoded size."

A block of code is set as follows:

message_bytes= message.encode("UTF-8")
bits_list = list(to_bits(c) for c in message_bytes )
len_h, len_l = divmod( len(message_bytes), 256 )
size_list = [to_bits(len_h), to_bits(len_l)]
bit_sequence( size_list+bits_list )

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

w, h = ship.size
for p,m in enumerate( bit_sequence(size_list+bits_list) ):
    y, x = divmod( p, w )
    r, g, b = ship.getpixel( (x,y) )
    r_new = (r & 0xfe) | m
    print( (r, g, b), m, (r_new, g, b) )
    ship.putpixel( (x,y), (r_new, g, b)  )

Any command-line input or output is written as follows:

$ python3.3 -m doctest ourfile.py

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "There is an Advanced Settings panel that defines these file associations."

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