how to use a Python function with keyword "self" in arguments

Question

i have a function that retrieve a list of stores in Python this functions is called :

class LeclercScraper(BaseScraper):
    """
        This class allows scraping of Leclerc Drive website. It is the entry point for dataretrieval.
    """
    def __init__(self):
        LeclercDatabaseHelper = LeclercParser
        super(LeclercScraper, self).__init__('http://www.leclercdrive.fr/', LeclercCrawler, LeclercParser, LeclercDatabaseHelper)


    def get_list_stores(self, code):
        """
            This method gets a list of stores given an area code

            Input :
                - code (string): from '01' to '95'
            Output :
                - stores :
                    [{
                        'name': '...',
                        'url'
                    }]

        """

when i try to write get_list_stores(92) i get this error :

get_list_stores(92)
TypeError: get_list_stores() takes exactly 2 arguments (1 given)

how can you help me with this ?

Try self.get_list_stores(92). It's like the this keyword in Java — inspectorG4dget
– inspectorG4dget, Commented Aug 27, 2013 at 18:29
Is this function in a class definition? It should be, but there aren't many contexts where you could actually call get_list_stores(92) without a NameError if it was in a class definition. — user2357112
– user2357112, Commented Aug 27, 2013 at 18:31
Yes, like Jim said, self is not a keyword. It could have whatever name you want. self is just a convention. — Gustavo Barbosa
– Gustavo Barbosa, Commented Aug 27, 2013 at 18:35
It looks like it takes a string, and you are passing it an int. Could that be a problem as well? — Jiminion
– Jiminion, Commented Aug 27, 2013 at 18:45

Óscar López · Accepted Answer · 2013-08-27 18:39:24Z

44

If the function is inside a class (a method), write it like this:

def get_list_stores(self, code):

And you have to call it over an instance of the class:

ls = LeclercScraper()
ls.get_list_stores(92)

If it's outside a class, write it without the self parameter:

def get_list_stores(code):

Now it can be called as a normal function (notice that we're not calling the function over an instance, and it's no longer a method):

get_list_stores(92)

edited Aug 27, 2013 at 18:39

answered Aug 27, 2013 at 18:32

Óscar López

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Comments

jsbueno · Accepted Answer · 2013-08-27 18:31:15Z

You don't use "self" arbitrarily - self is recommended to be the first parameter to functions which are written to be methods in classes. In that case, when it is invoked as a method, like in

class A(object):
    def get_list_stores(self,  code):
        ...

a = A()
a.get_listscores(92)

Python will insert the "self" parameter automatically on the call (and it will be the object named "a" in the outer scope)

Outside of class definitions, having a first parameter named "self" does not make much sense - although, as it is not a keyword it is not an error per se.

In your case, most likely,t he function you are trying to call is defined in class: you have to call it as an attribute of an instance of the class, and then you simply omit the first parameter - just like in the example above.

Community · Accepted Answer · 2017-05-23 11:46:38Z

4

If you are trying to use it in the class, access it like this:

self.get_listscores(92)

If you are trying to access it outside of the class, you need to first create an instance of LeclercScraper:

x = LeclercScraper()
y = x.get_listscores(92)

Also, self is not a keyword. It is simply the name chosen by convention to represent a class instance within itself.

Here's a good reference:

What is the purpose of self?

edited May 23, 2017 at 11:46

CommunityBot

11 silver badge

answered Aug 27, 2013 at 18:36

user2555451

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