TypeError in Python

Question

I have two classes for in case:

testing.py :

class Functions:
    def mapping(func, x):
        return func(x)

and I try to run the code below:

import testing

def doubleMe(data):
    return data * data

res = stream.Functions.map(testdouble, [1,2,3,4,5])
print res

After I try to run the code, I got the error

TypeError: unbound method mapping() must be called with Functions instance as first argument (got function instance instead)

I not too sure what what have went wrong here, can I have some advise? Thanks!

Kurt Spindler · Accepted Answer · 2012-11-02 16:28:14Z

3

Python functions always take the class or instance as the first argument of class functions/methods.

class Functions:
    def mapping(self, func, x):
        return func(x)

Alternatively, if you don't want to always create instances of the class, do the following to create a class method as opposed to an instance method.

class Functions:
    @classmethod
    def mapping(cls, func, x):
        return func(x)

The @ operator creates a function decorator, if it's a topic you'd like to google more.

answered Nov 2, 2012 at 16:28

Kurt Spindler

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Comments

mpenkov · Accepted Answer · 2012-11-02 16:30:40Z

1

I couldn't make much sense of your code (it seems incomplete, and names don't match up: mapping -> map, stream -> testing), but from the error message, it seems like you need to construct an instance of Function first. So you need something like:

func = stream.Functions()
func.map(testdouble, [1, 2, 3, 4, 5])

You also need to declare the map/mapping method properly (after deciding whether you want an instance or class method), as Kurt pointed out.

edited Nov 2, 2012 at 16:30

answered Nov 2, 2012 at 16:24

mpenkov

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