Global name not defined error in Python

Question

I am implementing my first class in Python and am struggling to make it work. I started with a very simple example:

#!/usr/bin/env python
"""

"""
import fetcher as fetcher
import fetchQueue as fetchQueue

    def __init__(self, seed = "a string"):
        self.seed = seed
        myFetchQueue = fetchQueue.FETCHQueue()

    def test(self):
        print "test"
        myFetchQueue.push(seed)
        myFetchQueue.pop()


#Entrance of this script, just like the "main()" function in C.
if __name__ == "__main__":
    import sys
    myGraphBuilder = GRAPHBuilder()
    myGraphBuilder.test()

and this class should call a method of another class I defined in a very similar way.

#!/usr/bin/env python
"""

"""

from collections import defaultdict
from Queue import Queue

class FETCHQueue():

    linkQueue = Queue(maxsize=0)
    visitedLinkDictionary = defaultdict(int)

    #Push a list of links in the QUEUE
    def push( linkList ):
        print linkList

    #Pop the next link to be fetched
    def pop():
        print "pop"

However when I run the code I get this output:

test Traceback (most recent call last):   File "buildWebGraph.py", line 40, in <module>
    myGraphBuilder.test()   File "buildWebGraph.py", line 32, in test
    myFetchQueue.push(seed) NameError: global name 'myFetchQueue' is not defined

So I guess that the construction of the object of class GRAPHBuilder and FETCHQueue is working, otherwise I would get an error before the string test gets outputed, but something else is going wrong. Can you help me?

Answer 1

def __init__(self, seed = "a string"):
    self.seed = seed
    myFetchQueue = fetchQueue.FETCHQueue()

Here, myFetchQueue is a local variable to the __init__ function. So, it will not available to other functions in the class. You might want to add it to the current instance, like this

    self.myFetchQueue = fetchQueue.FETCHQueue()

Same way, when you are accessing it, you have to access it with the corresponding instance, like this

    self.myFetchQueue.push(self.seed)
    self.myFetchQueue.pop()