Question

I’m a new Python programmer who is having a little trouble using ‘self’ in classes. For example:

class data:
    def __init__(self):
        self.table = []
    def add(self, file):
        self.table.append(file)
data.add('yes')

In this function I want to have table be a variable stored in the class data and use add to modify it. However, when I run this script it gives me the error:

Traceback (most recent call last):
  File "/Projects/Python/sfdfs.py", line 7, in <module>
    data.add('yes')
TypeError: add() takes exactly 2 positional arguments (1 given)

I assume that I am trying to call the function the wrong way in this instance, as this syntax is very similar to an example in the python documentation: http://docs.python.org/3.1/tutorial/classes.html

Answer 1

You first need to make an instance of the class:

mydata = data()

then you can call the method — on the instance, of course, not on the class:

mydata.add('yes')