Question

class Parser():
        html_escape_table = {
            "&": "&",
            '"': """,
            "'": "'",
            ">": ">",
            "<": "&lt;",
            }
        def html_escape(text):
            return "".join(html_escape_table.get(c,c) for c in text)
        def query():
            database = [x, y, z, etc, etc2]
            for x in database:
                html_escape(x)
                print x #for testing purposes
                return
test = Parser()

test.query()

Am I doing this correctly? I keep getting an error:

TypeError: query() takes no arguments (1 given)

I’m not seeing anywhere where I am passing an argument to query, or even to Parser.

Can someone explain what I am doing wrong here?

I tried calling just Parser.query() and got this error (this was after adding the self argument to all of my functions and object argument to my Parser class)

    Parser.query()
TypeError: unbound method query() must be called with Parser instance as first argument (got nothing instead)

Answer 1

Methods in classes require the argument self this is to do with parsing the instance to the method in how python does instance methods.

e.g.

class Test(object):
    def say_hello(self):
        print "Hi there"

Just to expand on this if you want to parse arguments to an instance method you still need self

class Test(object):
    def say_hello(self, name):
        print "Hi %s" % name

Edit:

Okay to explain it further you have to know how python handles instances, python handles instances in a very verbose and clear way, self is always used to refer to itself or this current instance, just like this in Java. So when python calls my_instance.method() its actually calling TheObject.method(my_instance) hence why self refers to the my_instance inside the method. That allows you to use the instance inside the method with the instance itself passed around inside the arugments.

Edit 2:

Even when you have self as an argument to the methods you need to call it from an instance like so

my_parser = Parser()
my_parser.method()

Edit 3:

This isn’t Java you don’t have to bind your functions together as methods inside a class, just leave them as free-roaming functions inside a parser.py file then you can do

import parser
parser.do_this()