Stuck in Python official tutorial docs

Question

A piece of Python code that expects a particular abstract data type
can often be passed a class that emulates the methods of that data
type instead. For instance, if you have a function that formats some
data from a file object, you can define a class with methods read()
and readline() that get the data from a string buffer instead, and
pass it as an argument.

Instance method objects have attributes, too: m.__self__ is the
instance object with the method m(), and m.__func__ is the
function object corresponding to the method.

I am stuck at Python tutorial doc, I can’t understand above docs. Can anyone explain it in a plain way?
with demo will be great. Some concept in python is very unfamiliar to me, I can’t get the meaning of author.

Asked By: Anson Hwang

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Answer 1

A piece of Python code that expects a particular abstract data type can often be passed a class that emulates the methods of that data type instead. For instance, if you have a function that formats some data from a file object, you can define a class with methods read() and readline() that get the data from a string buffer instead, and pass it as an argument.

Consider something like this.

def get_first_line_twice(file):
    line = file.readline()
    return line + line

This is "A piece of Python code that expects a particular abstract data type". "a particular abstract data type" is, in this case, a file.

"a class that emulates the methods of that data type instead" means a class that also has a readline() method that behaves similarly. E.g.

class Foo:
    def readline(self):
        return "foo"

We can pass an instance of Foo instead of a file to our function, and it will work without errors. That’s what the paragraph means.

Instance method objects have attributes, too: m.__self__ is the instance object with the method m(), and m.__func__ is the function object corresponding to the method.

Consider the Foo class from previous example.

f = Foo()
f.readline #the method

f #"the instance object with the method"
f.readline.__self__ is f #True

f.readline.__func__ #"the function object corresponding to the method"

The last line essentially returns readline decoupled from f. If we want to call it, we will actually need to pass an object as the self parameter, i.e. f.readline.__func__(f). Or f.readline.__func__(some_other_object). This can be useful for advanced functional programming, or maybe reflection. As a beginner, you can ignore these attributes for now.

Answered By: koobo

Stuck in Python official tutorial docs

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