How did my variable turn into a function?-CodePudding

Hello fellow S Overflowers. This question might seem dumb to some, but I cannot express how much asking these conceptual questions has helped me understand coding in general and for that I want to preface the question saying I appreciate all of you very much!!

My doubt here is: How did the variable Twice at the end, turned into a function call to which I could put parentheses on. How could a variable start behaving as a function?

Apologies if this is obvious to some, but I'd love some human explaining because being new to the scene, documentation jargon gets pretty complicated.

#Define echo
def echo(n):
    """Return the inner_echo function."""

    # Define inner_echo
    def inner_echo(word1):
        """Concatenate n copies of word1."""
        echo_word = word1 * n
        return echo_word

    # Return inner_echo
    return(inner_echo)

#Call echo: twice        
twice = echo(2)
    
#Call twice() and print
print(twice('hello'))

CodePudding user response：

In the echo function, you are returning inner_echo, which is pointer to a function, not its return value. In order to return the output of inner_echo you need to call it.

...
    # Return inner_echo value
    return(inner_echo(word))
...

You returned the nested function object, so twice becomes function object of inner_echo encapsulated in the enviroment from which it was returned. It means python saves the n variable, which does not exist inside inner_echo and twice becomes inner_echo function with given n value (2 in your example).

This would be unsafe code in other languages, which don't save the eviroment variables, however python does this implicitly.

CodePudding user response：

In Python variables can hold numbers, strings, functions, objects, even modules. You can put just about anything in a variable.

When you do return(inner_echo), inner_echo is a function. That's how you ended up with a function. If you did return(inner_echo(word1)), then the variable twice would end up containing 'hellohello' which might be more in line with what you're expecting.