This repository contains the Python code for:

Learning Algorithms: A Programmer's Guide to Writing Better Code
http://oreil.ly/learn-algorithms
George T. Heineman
ISBN: 978-1-49-209106-6

Each chapter has its own folder containing the code for that chapter. All Python code conforms to Python 3.4 and has been tested to work as far back as Python 3.3. While the core algorithms presented in the book will continue to work with earlier versions of Python, some code used to generate the tables and images in the book will not compile properly because of changes to Python libraries.

Chapter structure

In addition to the code related to a chapter, each folder contains three specific Python scripts:

• book.py - Generates the tables and data used for figures in the book
• challenge.py - Contains the solutions for the challenge exercises at the end of each chapter
• timing.py - Scripts that may take a significant amount of time to complete are pulled out separately
• test.py - test cases to validate the algorithms and supporting methods.

A separate algs folder contains Python scripts that are shared across the different chapters.

Documentation

The code documentation style follows standard Python documentation style. The supporting scripts (i.e., book.py, timing.py, test.py) typically have no documentation.

Sample output for all executions is provided in doc folder.

Resources

A dictionary of 321,129 English words is provided in the words.english.txt file and is used to provide sample inputs throughout the book.

A TMG graph file containing a representation of highways in Massachusetts is graciously provided by James Teresco from https://travelmapping.net/graphs

Installation

First make sure Python3 is installed on your system. The following steps show how to install Python on a windows operating system even if you do not have administrator privileges:

1. Download MSI file from python web site

   https://www.python.org/ftp/python/3.3.0/python-3.3.0.amd64.msi for example is
   what you would do to install Python 3.3.0, which is the earliest version for
   which this code base is compatible. Please consider using the latest version

2. Invoke MSI installer from command line, using the command as suggested by the
   older Python2.4 documentation (https://www.python.org/download/releases/2.4/msi/)

   msiexec /a python-3.3.0.amd64.msi TARGETDIR=C:\YOUR\DESTINATION\FILE

3. Now switch to the directory which contains the LearningAlgorithms code base.

4. modify launch.bat to update proper location for 'python3'

   C:\YOUR\DESTINATION\FILE\Python33\python.exe

Dependencies

The code depends on numpy, scipy and networkx. If these libraries are not installed, the scripts continue to operate in degraded fashion.

numpy and scipy are only used to model and perform analysis on data and runtime performance. networkx is used to construct graphs, and if this library is not installed, a replacement graph structure is used which is not efficient or suitable for production use.

Images

All of the tables in the book are reproducible from the Python book.py scripts found in each chapter. Many of the images will also be generated from these tables: these generates files are placed (by chapter number) within the images directory.

Testing

You can generate code coverage reports for the test cases after you install the coverage module with:

pip install coverage

Then in the top directory, execute the following commands to generate code coverage data and then present it as an HTML directory (found in htmlcov). Make sure your PYTHONPATH includes the current directory. There is a .coveragerc file that ensures only the book code is targeted. If you have not installed the coverage module, then replace each "coverage run" below with just "python3" and remove the "-a" command line option, which is there just to ask coverage to append coverage data across multiple runs.

coverage run -m unittest discover
coverage run -a book.py
coverage html

The test cases execute within 15 minutes or so. The book takes up to six hours to fully run, since it generates all tables and data for figures in the book. If you want to complete all timing results, then add those as well:

coverage run -a ch01/timing.py
coverage run -a ch02/timing.py
coverage run -a ch03/timing.py
coverage run -a ch04/timing.py
coverage run -a ch05/timing.py
coverage run -a ch07/timing.py

Each chapter has challenge exercises that have been completely solved, these can be executed from each chNN/challenge.py file.

The coverage.bat executable performs full coverage and takes about eight hours to complete.

Statistics

The following code statistics are generated using the cloc tool (https://github.com/AlDanial/cloc), excluding the ch03\perfect directory which contains the generated Python code for perfect hashtables.

perl cloc-1.86.pl LearningAlgorithms --exclude-dir=perfect,htmlcov

 121 text files.
 120 unique files.
  10 files ignored.

Language	files	blank	comment	code
Python	107	3112	3444	11919
Markdown	1	44	0	107
DOS Batch	2	11	6	45
XML	2	0	0	25
Bourne Shell	1	6	2	23
SUM:	113	3173	3452	12119

github.com/AlDanial/cloc v 1.86 T=0.38 s (293.9 files/s, 48759.3 lines/s)

Executable programs

Aside from the book.py, challenge.py, test.py and timing.py scripts that can be
found in each chapter, there are some standalone Python scripts that can be executed:

• ch03.perfect - computes a perfect hash table for its input.
• ch03.base26 - computes base26() computations shown in chapter 3.
• cho3.months - prints the examples from chapter 3 .
• ch07.maze - visualizes the maze in Figure 7-3. Feel free to change parameters to visualize mazes of different size.
• ch07.replacement - runs test cases for the replacement code for networkx.
• ch07.search - visualize result of Breadth First Search on sample maze.
• ch07.solver_bfs - animates Breadth First Search on a larger maze. Change parameter refresh_rate to 0.001 to slow down.
• ch07.solver_dfs - animates Depth First Search on a larger maze. Parameter refresh_rate is 0.001 so you can see its execution.
• ch07.solver_guided - animates Guided Search on a larger maze. Parameter refresh_rate is 0.001 so you can see its execution.
• ch07.spreadsheet - simulates a small spreadsheet application with 5 columns and 3 rows. Formulas can be infix expressions with parentheses.
• ch07.tmg_load - loads Massachusetts highway data set and visualizes waypoints and highway segments.
• ch07.viewer - visualizes a 50x50 rectangular maze with salt of 0.05. Change to 0 and results is a perfect rectangular maze.
• ch07.xlsx_example - application loads up an actual (though small) XLSX document containing the Fibonacci example from Figure 7-11.