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Underscores and Naming Conventions in Python

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Software engineers are known for having heated debates with each other on the different tools and technologies and their preferences. Yet they all agree on one specific thing, and that is consistency of code is vital.

Lack of the latter causes unpleasant troubles within teams (and even with one’s self) that makes everyone’s days a living hell.

Picture this: person A names their variables with styleA, person B with styleB and so on and so fourth.

Can you imagine how the code base would look like? It would be a wild jungle, making readability and maintainability pure fantasy!

For this purpose, naming conventions and styles were founded for a universal code that is standards compliant and therefore, less error-prone.

What is PEP8?

PEP8 is a style guideline that provides conventions for Python code which helps us with writing clean code.

This style guide is kept up-to-date as the language evolves, adding conventions and removing other ones that became obsolete. So you should always be tuned in.

This is the official PEP8 Documentation and I highly recommend you take a look at it from time to time.

General conventions in Python

  • Variables names should not be a single letter uppercase i, a lowercase L or an uppercase O.

  • Variable names should not start with numbers or an uppercase letter.

  • All variable names should be in lowercase.

  • Long variable names should be separated with an underscore. This style is called snake-case, the style used in Python.

Class name examples: Fruit, Vegetable, CoolBeans…

  • All function names (except factory functions) should be in lowercase.

Note: factory functions are functions that return objects, thus behaving like class declarations.

  • Class and factory function names follow the PascalCase naming convention (first letter of every word is capitalized).
this_is_how_you_name_me = "comply now or perish"
style_name = "snake-case"


In Python, there is no such thing as a constant, everything that you declare can be modified and overwritten afterwards. We use variables that we don’t modify instead (smart I know).

So how do we distinguish between variables and “constants”?

We write constant names in snake-case and in capital letters:

PI = 3.14

And now getting to the underscores…

Note: underscores between words in a variable name do not hold any meaning!

Underscores and access modifiers

Underscores in Python are discussed in the scope of access modifiers.

Access modifiers (private and protected) in reality do not exist in Python.

So how do we encapsulate our data? Let’s see:

Protected access modifiers

Protected attributes/methods are prefixed with an underscore.

Protected members of a class can only be accessed either from within the class or from its sub-classes.

That is not the case with Python though; all protected members to Python are public.

Notice that:

class Something:
   _banana = "I am hungry..."

# "I am hungry..."
# The attribute should not
# have been displayed!

Private access modifiers

Private attributes/methods are prefixed with a dunder (remember? They’re double underscores)

Private members of a class can only be accessed from within the class.

Now how the Python interpreter deals with this is very interesting!

class SomethingElse:
    __me_is_back = "Am I private?"

x = SomethingElse()
# Raises error AttributeError

So what are you talking about? It clearly is private! We couldn’t access it from outside of the class!

Here is the fun part!

The Python interpreter performs name mangling in such a way that makes it seem as if the member is indeed private.

Let’s look at the namespace (attributes and methods) of the object x of class SomethingElse using the dir() method:

Screenshot from 2021-03-21 19-52-15.png

Look at the first element of the list!

So basically we can just:

# "Am I private?"

We just accessed a private member from outside the class.

Underscores and keywords

If you end up in a situation where you need to name your variables with a reserved keyword, the convention says that you should prefix the name with an underscore:

def_ = "Ran out of creativity?"

Oh any by the way, if you wish to view all Python’s keywords:

from keyword import kwlist

Underscores and magic methods

Magic methods is a fancy name for special Python functions with a fixed name that are by convention enclosed with dunders.

We’ve seen in a previous example one of them being __init__

To state other magic methods, we have: __add__ , __str__ , __and__

Thank you for reading!

That was it! I hope you learned something new and enjoyed reading!

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Have a nice one!

Thumbnail picture by Alvaro Reyes on Unsplash