Article series: 5 Clean Coding Tips – 2. Name Variables in a Meaningful Way

This is the second of the article series “5 tips for clean coding” to follow as soon as you’ve made the first steps into your coding career, in this article series. Read the introduction here, to find out why it is important to write clean code if you missed it.

When it comes to naming variables, there are a few official rules in the PEP8 style guide. A variable must start with an underscore or a letter and can be followed by a number of underscores or letters or digits. They cannot be reserved words: True, False, or, not, lambda etc. The preferred naming style is lowercase or lowercase_with_underscore. This all refers to variable names on a visual level. However, for readability purposes, the semantic level is as important, or maybe even more so. If it was for python, the variables could be named like this:

b_a327647_3 = DataFrame() 
hw_abc7622 = DataFrame()  
a10001_kkl = DataFrame()

It wouldn’t make the slightest difference. But again, the code is not only for the interpreter to be read. It is for humans. Other people might need to look at your code to understand what you did, to be able to continue the work that you have already started. In any case, they need to be able to decipher what hides behind the variable names, that you’ve given the objects in your code. They will need to remember what they meant as they reappear in the code. And it might not be easy for them.

Remembering names is not an easy thing to do in all life situations. Let’s consider the following situation. You go to a party, there is a bunch of new people that you meet for the first time. They all have names and you try very hard to remember them all. Imagine how much easier would it be if you could call the new girl who came with John as the_girl_who_came_with_John. How much easier would it be to gossip to your friends about her? ‘Camilla is on the 5^th glass of wine tonight, isn’t she?!.’ ‘Who are you talking about???’ Your friends might ask. ‘The_Girl_who_came_with_John.’ And they will all know. ‘It was nice to meet you girl_who_came_with_john, see you around.’ The good thing is that variables are not really like people. You can be a bit rude to them, they will not mind. You don’t have to force yourself or anyone else to remember an arbitrary name of a variable, that accidentally came to your mind in the moment of creation. Let your colleagues figure out what is what by a meaningful, straightforward description of it.

There is an important tradeoff to be aware of here. The lines of code should not exceed a certain length (79 characters, according to the PEP 8), therefore, it is recommended that you keep your names as short as possible. It is worth to give it a bit of thought about how you can name your variable in the most descriptive way, keeping it as short as possible. Keep in mind, that
the_blond_girl_in_a_dark_blue_dress_who_came_with_John_to_this_party might not be the best choice.

There are a few additional pieces of advice when it comes to naming your variables. First, try to always use pronounceable names. If you’ve ever been to an international party, you will know how much harder to remember is something that you cannot even repeat. Second, you probably have been taught over and over again that whenever you create a loop, you use i and j to denote the iterators.

for i in m:
    for j in n:

It is probably engraved deep into the folds in your brain to write for i in…. You need to try and scrape it out of your cortex. Think about what the i stands for, what it really does and name it accordingly. Is i maybe the row_index? Is it a list_element?

for element in list_of_words:
    for letter in word:

Additionally, think about when to use a noun and where a verb. Variables usually are things and functions usually do things. So, it might be better to name functions with verb expressions, for example: get_id() or raise_to_power().

Moreover, it is a good practice to name constant numbers in the code. First, because when you name them you explain the meaning of the number. Second, because maybe one day you will have to change that number. If it appears multiple times in your code, you will avoid searching and changing it in every place. PEP 8 states that the constants should be named with UPPER_CASE_NAME. It is also quite common practice to explain the meaning of the constants with an inline comment at the end of the line, where the number appears. However, this approach will increase the line length and will require repeating the comment if the number appears more than one time in the code.

Emilia Cheladze

Emilia Cheladze is a Data Scientist with a background in neuroscience, who is passionate about exploring business insights. Before she started working for DATANOMIQ she received M. Sc. from the Berlin School of Mind and Brain, Humboldt Universität zu Berlin and a B. Sc. in Cognitive Science from Nicolaus Copernicus University in Torun, Poland.