I’m a Rubyist learning Python and I’m wondering if there is a convention in Python along the lines of the following.

In Ruby, methods that return booleans are supposed to always end in a ?. For example,

def palindrome?(string)
  # some code that tests whether string is a palindrome
end

The only existing SO question I can find speaking to this does not provide a definitive answer.

There is no standard naming convention specific to boolean-returning methods. However, PEP8 does have a guide for naming functions.

Function names should be lowercase, with words separated by
underscores as necessary to improve readability.

Typically, people start a function with is (e.g. is_palindrome) to describe that a boolean value is returned.

I concur with @CarolChen on the principle of turning to PEP8, the Python Style Guide, for guidance. I will suggest however that “as necessary to improve readability” is in the eye of the beholder. For example, each of these functions are used in Python either as functions of the str object or as builtin functions. These are as fundamental as it gets in the Python ecosystem and are good examples of a usage style focused on returning a boolean state AND having easily readable function names.

str. methods

isalnum()
isalpha()
isdecimal()
isdigit()
isidentifier()
islower()
isnumeric()
isprintable()
isspace()
istitle()
isupper()

builtin functions:

isinstance()
issubclass()

You can define it like

def is_palindrome(variable):
    # your logic\
    # return True / False