What is first class function in Python

Question

I am still confused about what first-class functions are. If I understand correctly, first-class functions should use one function as an object. Is this correct?

Is this a first-class function?

def this_is_example(myarg1):     return myarg1  def this_is_another_example(myarg):     return this_is_example(myarg) + myarg  this_is_another_example(1) 

Answer 1

A first-class function is not a particular kind of function. All functions in Python are first-class functions. To say that functions are first-class in a certain programming language means that they can be passed around and manipulated similarly to how you would pass around and manipulate other kinds of objects (like integers or strings). You can assign a function to a variable, pass it as an argument to another function, etc. The distinction is not that individual functions can be first class or not, but that entire languages may treat functions as first-class objects, or may not.

Answer 2

"First-Class Functions" (FCF) are functions which are treated as so called "First-Class Citizens" (FCC). FCC's in a programming language are objects (using the term "objects" very freely here) which:

• Can be used as parameters
• Can be used as a return value
• Can be assigned to variables
• Can be stored in data structures such as hash tables, lists, ...

Actually, very roughly and simply put, FCF's are variables of the type 'function' (or variables which point to a function). You can do with them everything you can do with a 'normal' variable.

Knowing this, both this_is_another_example(myarg) and this_is_example(myarg1) are First-Class Functions, since all functions are First-Class in certain programming languages.