Python you want a string you get a tuple – howzat ?

Summary

How come you’re getting a tuple when you passed a string ?

Don’t do this at home

This is something that happened to me today. It really perplexed me so maybe this post will help someone else.

My class

I’d got a class a bit like the one below:

class cat(object):
    def __init__(self, name, colour, weight):
        self.name = name
        self.colour = colour,
        self.weight = weight
    def report(self):
        print self.name
        print self.colour
        print self.weight

Using it

But when I tried to use it like this:

mycat = cat('Garfield', 'Marmalade', 10)
mycat.report()

the output looked like this :

Garfield
('Marmalade',)
10

The problem being the attribute `colour` was being stored as a tuple.

The Answer

Looking back on it the problem is quite obvious but I was so busy looking at other parts of the situation (which was significantly more complex than the my cat example I missed it for quite a while.

Within the __init__ method I had inadvertently appended a comma onto the end of the self.colour assignment and Python takes that to mean, in our example, colour is the first element of a tuple.