Coding best practices
There are code standards and conventions available depending on the language you are using and sometimes also conventions adopted for specific collaborative projects. While below we provide a few links to these, here we are just going to focus on some basic tips that can help you making your code more readable and safer from bugs. These can be applied to any language.
- 1 Naming
- 1.1 Use descriptive names for variables and functions
- 1.2 Avoid reserved keywords and names of common functions
- 1.3 Use consistent naming across the code
- 1.4 Avoid hard-coding values
- 1.5 Define constant values only once, at the start of the code, or as part of a configuration file , or as arguments to your function or program.
- 1.6 This includes paths, or other string type variables, not just numbers. Defining all these values in one place, will make it easier to update them, without having to chnage a value in multiple places, it will reduce the chnace of errors. It will also make your code more readable, make your intentions clearer and the code will be more generic and faster to adapt for different configurations.
- 1.7 Initialising variables
- 2 Code structure
- 4 Order of precedence
- 5 Functions
- 6 Use tests
- 7 Style guides
Use descriptive names for variables and functions
There is no advantage in using short names for variables and functions, it is good practice instead to use names that are descriptive, even if this will make them longer. Particularly for functions it is good to specify in the name what they do.
For example for a function that calculates an anomaly use calculate_anomaly() rather than calc().This also reduce the chances of using a reserved word. NB If you're using an IDE to edit your code then you can easily auto complete the names
Avoid reserved keywords and names of common functions
Reserved keywords are words that are used for special functionalities, they change with the language but usually are used to control the flow of the code as "if", "for", "import" or used for declarations like "None", "True", "global, so they cannot be used to name anything else. Any other word can be used as a name but be careful, in dinamycally typed languages like Python a variable is evaluated while running the code, it is not declared at the start. This is because a variable name is just a link to an object and so the same name can refer to different objects in the same code.
For example if I have a function called mean and later on in the code assigned a float value to it.
I won't get an error then, but I will when trying to call mean as a function
#For example if I have a function called mean def mean(variable): ... return value mean = 45.3 #if I try then to call the function I will get an error sst_mean = mean(sst) #as "mean is now referring to the float object "45.3" as i have overwritten the link to the mean
mean type of variable can be are some that is still best to avoid, common examples are 'file'
There are also some that can be used as a name,like 'file', 'format', 'int', 'list', 'dict' , but that are already names of existing functions. This will of course also depend on which modules you are using and how you import them.
Use consistent naming across the code
Try to be consistent in the way you name your variables, constants and functions. There are different opionions on what is the best convention:
- CapitalisedWords (also known as CamelCase)
- ALL_CAPITALS usually used for constants values
Whatever you choose try to be consistent, use the same conventions for the same type of objects.
Avoid hard-coding values
Define constant values only once, at the start of the code, or as part of a configuration file , or as arguments to your function or program.
This includes paths, or other string type variables, not just numbers. Defining all these values in one place, will make it easier to update them, without having to chnage a value in multiple places, it will reduce the chnace of errors. It will also make your code more readable, make your intentions clearer and the code will be more generic and faster to adapt for different configurations.
Some languages like Python enforce indenting, but even where it is not necessary indenting your code can help outlining the code structure. Again try to be consistent either use tabs or spaces, some languages like python have a preference for spaces.
Comments are extremely useful to document what your code is doing. Again you do not need to comment every line, as that might actually made the code less redable. But it is a good practice to have:
- a block of comments at the start of the code listing author, license,a a date for the last update, what the code does and how to use it.
- similarly have a fe wlines of comments for each function or before a coherent block of code in the main program, for example before an "if/else" block.
It can also be useful starting a code by writing what do you want to do as comments. For example # Assign arguments # Open data files # Calculate ... # Plot ... # Save output to file
In this way you have a draft of your comments and you can work out the best structure, individuate blocks that can be included in a function etc, before you even start coding. It can save you a lot of time.
Use functions to organise your code / DRY code
Ideally a function should execute one coherent operation. As none of us it's a software developer we are not suggesting to transform every single line of code in a function, but try to inlcude in a function a logical block of lines. This is particularly true and useful if it's a block of code you might want to repeat in other parts of this same or others programs. Another good reason to enclose a block of code in a function it is to make it easier to add a test.
One statement per line
Cramming a lot of instructions in one line of code won't make your code faster, just less readable. It will also make it more difficult to pinpoint what is causing an error if you have a few instructions in the same line.
Keep your files a reasonable length
Main message here is to be consistent and descriptive, in the end any conventions aim is to have consistency. Even if you are not using an established convention, being at least consistent across all of your codes will help making them more readable and re-usable.
Order of precedence
make your intentions clear even if it is not necessary
Clear flow: try to have only one exit point in a function
It is a good idea to test at least critical parts of your code. You want to be sure that a calculation which is critical to your results, is producing consistent and correct results, no matter what changes you introduce to the same function or other part of your code. No matter how many tests you are conducting it is hard to preview all the possible ways a code can be used and it is often the case that as soon as you sue a different set of data you are going to find some bugs. Every time you fix a bug make sure you are adding a test to capture it. So you will know if accidentally you re-introduce it later on.
- Python: pep8 Python Enhancement Proposal
- Python reserved keywords
- Julia: style guide
- R style guide
- R reserved keywords
This page was inspired by the seminar "Reproducible research how to write code that is built to last organised by DataTas. A recording is available on their facebook page.