pep8.org | - PEP 8 , for Humans | Dataset library

Though you may not commonly see this, it is not bad practice; although, it does have specific use cases.

Normally methods can be broken into two parts, its public version and its private version. The public method basically adds an API layer which can then decide which private method to call or do some data manipulation on the inputs to conform it to meet the private methods requirements. The private method deals with handling the class private attributes themselves.

Adding this separation layer can be convenient.

Here is a basic example just to illustrate the idea. Though for something this simple you can just do it all in the single method.