Calling a Method in Python more Efficiently

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

In the online version of Learn Python The Hard Way they have:

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

for the test, which suggests that you don't need a lexicon class, but a lexicon.py file with a scan function to test.

And it's spelled instantiating (as in I'm making an instance of this class).

• Steve Narrow: Ah yes, my bad there, I didn't copy paste the original, but the modified and deleted the extra lines. Thank you.
• Steve Narrow: And I tried this out too, using a lexicon.py file and changed the import. Works as well. Muchas.

Answer 2

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

• Steve Narrow: This worked with a little modification: def scan(data): Thanks much. :)