Practical Python Programming - Instructor Notes

Author: David Beazley

Overview

This document provides some general notes and advice on teaching the content of my “Practical Python” course including objectives, target audience, tricky bits, etc.

These instructions were given to people teaching the course in a typical three-day corporate training environment. They might give you some insight about teaching your own course.

Target Audience and General Approach

This course is intended to be an “Introduction to Python” course for people who already have some programming experience. This is definitely not a course designed to teach people “programming 101.”

Having said that, I have observed that the typical student in a Python course is also not likely to be a hard-core software engineer or programmer. Instead, you are probably going to get a mix of engineers, scientists, web programmers, and more inexperienced developers. Student background varies widely. You might have some students with a lot of C,C++, Java experience, others might know PHP and HTML, others may be coming from tools like MATLAB, and others still might have almost no traditional “programming” experience at all despite my best attempts to make the prerequisites clear.

With this in mind, the course aims to teach Python through the general problem of manipulating data (stock market data in particular). This domain has been chosen because it’s simple and something everyone should know about it regardless of their background. Just as an example, students with weak programming skills are still likely to know about common things like using a spreadsheet (e.g., Excel). So, if they’re really stuck, you can tell them things like “well, this list of tuples is kind of like rows of data in a spreadsheet” or “a list comprehension is the same idea as applying an operation to a spreadsheet column and putting the result in a different column.” The key idea is to stay grounded in a real-world setting as opposed to getting sidetracked into esoteric “computer science” problems (e.g., “let’s go compute fibonacci numbers.”).

This problem domain also works well for introducing other programming topics. For example, scientists/engineers might want to know about data analysis or plotting. So, you can show them how to make a plot using matplotlib. Web programmers might want to know how to present stock market data on a web-page. So, you can talk about template engines. Sysadmins might want to do something with log files. So, you can point them at a log file of real-time streaming stock data. Software engineers might want to know about design. So, you can have them look at ways to encapsulate stock data inside an object or making a program extensible (e.g., how would make this program produce output in 10 different table formats). You get the idea.

Presentation Guidelines

The presentation slides (notes) are there to provide a narrative structure to the course and for reference by students when they work on exercises. Do not laboriously go over every bullet point on every slide--assume that students can read and that they will have time to go back when coding. I tend to go through the slides at a pretty brisk pace, showing short examples interactively as I go. I often skip slides entirely in favor of live demos. For example, you don't really need to do a bunch of slides on lists. Just go to the interpreter and do some list examples live instead. Rule of thumb: No more than 1 minute per slide unless it’s something unusually tricky. Honestly, you could probably skip most of the slides and simply lecture using live demos if you feel that it works for you. I often do this.

Course Exercises

The course has about 130 hands-on exercises. If you do every single exercise and give students time to think and code, it will likely take them about 10-12 hours. In practice, you will probably find that students require more time on certain exercises. I have some notes about this below.

You should repeatedly emphasize to students that solution code is available and that it is okay to look at it and copy it--especially due to time requirements.

Prior to teaching the course, I would strongly advise that you go through and work every single course exercise so that there are no surprises.

During course delivery, I usually work every single exercise from scratch, without looking at the solution, on my computer while the students also work. For this, I strongly advise you to have a printed copy of the exercises on hand that you can look at without having to pull it up on the computer screen (which is being projected). Near the end of the exercise time period, I will start discussing my solution code, emphasizes different bits on the screen and talking about them. If there are any potential problems with the solution (including design considerations), I’ll also talk about it. Emphasize to students that they may want to look at/copy solution code before going forward.

Section 1: Introduction

The major goal of this section is to get people started with the environment. This includes using the interactive shell and editing/run short programs. By the end of the section, students should be able to write short scripts that read data files and perform small calculations. They will know about numbers, strings, lists, and files. There will also be some exposure to functions, exceptions, and modules, but a lot of details will be missing.

The first part of this course is often the longest because students are new to the tools and may have various problems getting things to work. It is absolutely critical that you go around the room and make sure that everyone can edit, run, and debug simple programs. Make sure Python is installed correctly. Make sure they have the course exercises downloaded. Make sure the internet works. Fix anything else that comes up.

Timing: I aim to finish section 1 around lunch on the first day.

Section 2 : Working with Data

This section is probably the most important in the course. It covers the basics of data representation and manipulation including tuples, lists, dicts, and sets.

Section 2.2 the most important. Give students as much time as they need to get exercises working within reason. Depending on audience, the exercises might last 45 minutes. In the middle of this exercise, I will often move forward to Section 2.3 (formatted printing) and give students more time to keep working. Together, Sections 2.2/2.3 might take an hour or more.

Section 2.4 has people explore the use of enumerate(), and zip(). I consider these functions essential so don’t skimp on it.

Section 2.5 introduces the collections module. There is a LOT that could be said about collections, but it won't be fully appreciated by students at this time. Approach this more from the standpoint of "here's this cool module you should look at later. Here are a few cool examples."

Section 2.6 introduces list comprehensions which are an important feature for processing list data. Emphasize to students that list comprehensions are very similar to things like SQL database queries. At the end of this exercise, I often do an interactive demo involving something more advanced. Maybe do a list comprehension and plot some data with matplotlib. Also an opportunity to introduce Jupyter if you're so inclined.

Section 2.7 is the most sophisticated exercise. It relates to the use of first-class data in Python and the fact that data structures like lists can hold any kind of object that you want. The exercises are related to parsing columns of data in CSV files and concepts are later reused in Section 3.2.

Timing: Ideally, you want to be done with section 2 on the first day. However, it is common to finish with section 2.5 or 2.6. So, don't panic if you feel that you're a bit behind.

3. Program Organization

The main goal of this section is to introduce more details about functions and to encourage students to use them. The section builds from functions into modules and script writing.

Section 3.1 is about going from simple “scripting” to functions. Students should be discouraged from writing disorganized “scripts.” Instead, code should at least be modularized into functions. It makes the code easier to understand, it makes it easier to make changes later, and it actually runs a little bit faster. Functions are good.

Section 3.2 is probably the most advanced set of exercises in the whole course. It has students write a general purpose utility function for parsing column-oriented data. However, it makes heavy use of list comprehensions as well as lists of functions (e.g., functions as first-class objects). You will probably need to guide people through every single step of this code, showing how it works in great detail. The payoff is huge however---you can show people a short general purpose function that does something amazingly powerful and which would be virtually impossible to write in C, C++, or Java without having a LOT of very complicated code. There are a lot of possible design/discussion avenues for this code. Use your imagination.

Section 3.3 adds error handling to the function created in Section 3.2 This is a good time to talk about exception handling generally. Definitely talk about the dangers of catching all exceptions. This might be a good time to talk about the “Errors should never pass silently” item on the “Zen of Python.”

*Note: Before Exercise 3.4, make sure students get fully working versions of report.py, pcost.py, and fileparse.py. Copy from Solutions folder if needed *

Section 3.4 Introduces module imports. The file written in Section 3.2-3.3 is used to simplify code in Section 3.1. Be aware that you may need to help students fix issues with IDLE, sys.path, and other assorted settings related to import.

Section 3.5 talks about __main__ and script writing. There's a bit about command line arguments. You might be inclined to discuss a module like argparse. However, be warned that doing so opens up a quagmire. It's usually better to just mention it and move on.

Section 3.6 opens up a discussion about design more generally in Python. Is it better to write code that's more flexible vs code that's hardwired to only work with filenames? This is the first place where you make a code change and have to refactor existing code.

Going forward from here, most of the exercises make small changes to code that's already been written.

4. Classes and Objects

This section is about very basic object oriented programming. In general, it is not safe to assume that people have much background in OO. So, before starting this, I usually generally describe the OO “style” and how it's data and methods bundled together. Do some examples with strings and lists to illustrate that they are “objects” and that the methods (invoked via .) do things with the object. Emphasize how the methods are attached to the object itself. For example, you do items.append(x), you don’t call a separate function append(items, x).

Section 4.1 introduces the class statement and shows people how to make a basic object. Really, this just introduces classes as another way to define a simple data structure--relating back to using tuples and dicts for this purpose in section 2.

Section 4.2 is about inheritance and how you use to create extensible programs. This set of exercises is probably the most significant in terms of OO programming and OO design. Give students a lot of time to work on it (30-45 minutes). Depending on interest, you can spend a LOT of time discussing aspects of OO. For example, different design patterns, inheritance hierarchies, abstract base classes, etc.

Section 4.3 does a few experiments with special methods. I wouldn't spend too much time fooling around with this. Special methods come up a bit later in Exercise 6.1 and elsewhere.

Timing: This is usually the end of the 2nd day.

5. Inside Objects

This section takes students behind the scenes of the object system and how it’s built using dictionaries, how instances and classes are tied together, and how inheritance works. However, most important part of this section is probably the material about encapsulation (private attributes, properties, slots, etc.)

Section 5.1 just peels back the covers and has students observe and play with the underlying dicts of instances and classes.

Section 5.2 is about hiding attributes behind get/set functions and using properties. I usually emphasize that these techniques are commonly used in libraries and frameworks--especially in situations where more control over what a user is allowed to do is desired.

An astute Python master will notice that I do not talk about advanced topics such as descriptors, or attribute access methods (__getattr__, __setattr__) at all. I have found, through experience, that this is just too much mental overload for students taking the intro course. Everyone’s head is already on the verge of exploding at this point and if you go talk about how something like descriptors work, you’ll lose them for the rest of the day, if not the rest of the course. Save it for an "Advanced Python" course.

If you're looking at the clock thinking "There's no way I'm going to finish this course", you can skip section 5 entirely.

6. Generators

The main purpose of this section is to introduce generators as a way to define custom iteration and to use them for various problems related to data handling. The course exercises have students analyze streaming data in the form of stock updates being written to a log file.

There are two big ideas to emphasize. First, generators can be used to write code based on incremental processing. This can be very useful for things like streaming data or huge datasets that are too large to fit into memory all at once. The second idea is that you can chain generators/iterators together to create processing pipelines (kind of like Unix pipes). Again, this can be a really powerful way to process and think about streams, large datasets, etc.

Some omissions: Although the iteration protocol is described, the notes don’t go into detail about creating iterable objects (i.e., classes with __iter__() and next()). In practice, I’ve found that it’s not necessary to do this so often (generators are often better/easier). So, in the interest of time, I’ve made a conscious decision to omit it. Also not included are extended generators (coroutines) or uses of generators for concurrency (tasklets, etc.). That’s better covered in advanced courses.

7. Advanced Topics

Basically this section is an assortment of more advanced topics that could have been covered earlier, but weren’t for various reasons related to course flow and content of the course exercises. If you must know, I used to present this material earlier in the course, but found that students were already overloaded with enough information. Coming back to it later seems to work better---especially since by this point, everyone is much more familiar with working in Python and starting to get the hang of it.

Topics include variadic function arguments (*args, **kwargs), lambda, closures, and decorators. Discussion of decorators is only a tiny hint of what’s possible with metaprogramming. Feel free to say more about what’s possible, but I’d probably stay out of metaclasses! Lately, I have been demoing "numba" as an example of a more interesting decorator.

If you're pressed for time, most of section 7 can be skipped or heavily compressed (you could skip exercises for instance).

8. Testing and Debugging

The main purpose of this section is just to introduce various tools and techniques related to testing, debugging, and software development. Show everyone the unittest module. Introduce the logging module. Discuss assertions and the idea of “contracts.” Show people the debugger and profiler. Most of this is self-explanatory.

9. Packages

At this point, students have written an assortment of files (pcost.py, report.py, fileparse.py, tableformat.py, stock.py, portfolio.py, follow.py, etc.). Two main goals in this section. First, put all of the code into a Python package structure. This is only a gentle introduction to that, but they'll move the files into a directory and everything will break. They'll need to fix their import statements (package relative imports) and maybe fiddle with an __init__.py file. Second goal, write a simple setup.py file that they can use to package up the code and give it away to someone. That's it. End of the course.

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