Catch errors and handle them in your app.

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In this article we will look at exceptions:

This article is taken from my book Python Quick Start.

Program errors

Computer programs sometimes go wrong. There are three broad types of error you will encounter when you are writing code:

Syntax errors occur when the code you type in isn’t valid. This is often due to typing errors or misunderstanding Python syntax. For example:

s = [1, 2, 3 # Missing end bracket 1a = 3 #…


Optimize list and string manipulation using slice notation.

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Slicing allows us to access part of a list or other sequence. In this article we will see how to:

This article is from my book Python Quick Start.

Slicing a list

We already know how to obtain a list element by indexing:

k = [10, 20, 30, 40, 50]
print(k[1]) # 20

Of course, k[1] references element number 1 of list k, which is the second element because elements are numbered…


Making your plots zing.

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Matplotlib allows you to control many aspect of your graphs. In this article we will see how to style line plots. This includes

You can choose to plot data points using lines, or markers, or both.

Matplotlib has a simple notation to set the colour, line style and marker style using a coded text string, for example ‘r:’ creates a red, dottedline. …


OSS for fun and profit

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This article is a quick guide on how to create and run your own open-source project. Specifically, it assumes it will be a Python project, although many of the things covered here can be applied to other types of project.

This isn’t a guide on how to set up a GitHub account and commit your first source files. Instead, it focusses on the wider whys and hows of open source development, and will hopefully help you to avoid the common pitfalls.

Why do it?

People create open-source software for many different reasons.

Quite often, a developer will decide to create a piece of…


What I learned from writing three Python books in a year

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Over the past year or so, I have written three e-books on various topics in Python programming. Although I certainly don’t consider myself to be an expert on self-publishing, I have learned a bit in this time, so I will share it here. I hope you might find it useful.

This article covers four stages:

I have found the whole process takes me about 3 months, if I put most of my hobby time…


Process images in 3 lines of Python

Pillow is a versatile and popular Python imaging library. The ImageEnhance module is a particularly useful module within Pillow. It can be used to adjust colour, contrast, brightness and sharpness in a few simple lines of code.

_Enhance interface

Each image enhance function is implemented as an object that implements the _Enhance interface. The interface provides a single method:

enhance(factor)

For example, the ImageEnhance.Brightness class controls the brightness of an image, It has an enhance method that it inherits from _Enhance.

factor is a number that controls the effect. For example, for Brightness a factor


Easy animation with generativepy

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generativepy makes it very easy to create animated GIFs. This can be done with a simple script, and usually results in a fairly well optimised GIf file.

The gif module makes use of the gifsicle application. This can be downloaded for free, and must be installed on your system in order for the gif module to work.

GIF images

GIF (Graphics Interchange Format) is a bitmap image format that was developed in the 1980s for transferring images over networks. …


Deriving new functions with functools

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Functional programming is a paradigm in which functions form the fundamental building blocks.

It should be no surprise that functional programming includes several techniques for deriving new functions from existing functions. This is analogous to object oriented programming, where classes are the building block, and we have various ways to derive new classes from existing ones (inheritance and composition, for example). In both cases, the aim is the same — to reuse existing code (following the DRY principle, don’t repeat yourself).

Partial application is one such technique.

What is partial application?

Here is a function that returns the value…


There are various ways of testing software, and unit testing is a vital part of the mix.

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It is, of course, vital to test software. There are various ways to test software, including:


Simple implementations of the List and Maybe monads.

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In the article on the Failure monad we looked at a simple definition of what a monad is:

A monad is a design pattern that allows us to add a context to data values, and also allows us to easily compose existing functions so that they execute in a context aware manner.

In this article we will look at two other common monads:

List monads

A List monad allows us to process lists of values, without cluttering our code with looping constructs.

How a List monad is used

As with the Failure monad, our List monad…

Martin McBride

I am a software developer with over 30 years experience in Java, Python and C++. I write for pythoninformer.com.

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