4 Jump the Five: Working with dictionaries

“When I get up, nothing gets me down.”

--D. L. Roth

In an episode of the television show The Wire, drug dealers assume the police are intercepting their text messages. Whenever a phone number needs to be texted in the course of a criminal conspiracy, the dealers will obfuscate the number. They use an algorithm we’ll call “Jump the Five” because each number is changed to its mate on the opposite of a US telephone pad if you jump over the 5. In this exercise, we’ll discuss how to encrypt messages using this algorithm, and then we’ll see how to use it to decrypt the encrypted messages, you feel me?

If we start with the 1 button and jump across the 5, we get to 9. The 6 jumps the 5 to become 4, and so forth. The numbers 5 and 0 will swap with each other.

In this exercise, we’re going to write a Python program called jump.py that will take in some text as a positional argument. Each number in the text will be encoded using this algorithm. All non-number text will pass through unchanged. Here are a couple of examples:

$ ./jump.py 867-5309
243-0751
$ ./jump.py 'Call 1-800-329-8044 today!'
Call 9-255-781-2566 today!

4.1 Dictionaries

4.1.1 Creating a dictionary

4.1.2 Accessing dictionary values

4 Jump the Five: Working with dictionaries

4.1 Dictionaries

4.1.1 Creating a dictionary

4.1.2 Accessing dictionary values

4.1.3 Other dictionary methods

4.2 Writing jump.py

4.3 Solution

4.4 Discussion

4.4.1 Defining the parameters

4.4.2 Using a dict for encoding

4.4.3 Various ways to process items in a series

4.4.4 (Not) using str.replace()

4.5 Going further

Summary