Question

I’m a newb working through Learn Python the Hard Way.

The point of this exercise is to write a word scanner for that passes the nosetests when run by a provided unit test.

While running nosetests on the following provided unit test I was getting this error:

`TypeError: unbound method scan() must be called with lexicon instance as first argument (got str instance instead)

Lesson-supplied Test

from nose.tools import *
from ex48 import lexicon

def test_directions():
    assert_equal(lex.scan("north"), [('direction', 'north')])
    result = lex.scan("north south east")
    assert_equal(result, [('direction', 'north'),
                          ('direction', 'south'),
                          ('direction', 'east)])

After some investigation I found here a user who is working through the same exercise:

nosetests, python

python variables, classes

The answer there suggested instantiating (instaniating?) the method inside the unit test. So I did the following modification and wrote up my class in file ex48.py and it passes nosetests.

Modified Test

from nose.tools import *
from ex48 import lexicon


def test_directions():
    lex = lexicon("north")
    assert_equal(lex.scan("north"), [('direction', 'north')])
    lex = lexicon("north south east")
    result = lex.scan("north south east")
    assert_equal(result, [('direction', 'north'),
                          ('direction', 'south'),
                          ('direction', 'east')]) 

ex48.py – Scanner

class lexicon(object):

    def __init__(self, data):
        #nosetests fails me if I don't put in some dummy
        # __init__ function with a dummy line, not sure why.
    self.direction = data

    def scan(self, data):
        split_data = data.split()
        directions = ['north', 'south', 'east', 'west']
        data_reply = []
        #for loop for the length of the list
        for split_data_item in split_data:
            #If data is in the directions list
            if split_data_item in directions:
                #Add [('direction', data)] to a dict
                data_reply.append(('direction', split_data_item))

        #Return the list
        return data_reply

I’m not sure if the unit test was meant to be changed. I found a clue about ‘directly intantiating an object’ here:

Python: does calling a method 'directly' instantiate the object?

But am not sure if this applies. Can a scanner be made to instantiate itself or is the provided unit test a trick ‘question’ and must be modified?

Answer 1

You should keep the test the way it was, and use a @staticmethod decorator on the scan method. This way, you’ll be able to call the method directly from the class without need to instanciate an object for this.

class lexicon(object):

   @staticmethod
   def scan(data):
      #do the stuff here