Python Using methods from other modules

Question

I have two modules called Dfs and Graph. In my Graph module, I have a class Graph and a method called ReadGraph. In my Dfs module, I have a method that calls on ReadGraph but I get the following error message when I type: Dfs.ProcessGraph(testcase.txt,verbose=True)

Error message: NameError: name 'testcase' is not defined

Could someone explain how to fix this?

Thanks.

From my Dfs.py module:

import sys 
from Graph import *

class Dfs( object ):

   def ProcessGraph(file_name, verbose):
      g=ReadGraph(file_name)

From my Graph.py module:

class Graph( object ):

   def ReadGraph( file_name ):

@jonrsharpe: At the top of my Dfs module I have: from Graph import * — Student
– Student, Commented Apr 25, 2014 at 6:52
Can you include a minimal code example that produces the error? — Tim
– Tim, Commented Apr 25, 2014 at 7:00
Is the indentation correct? Are the functions seperate from the classes? — Tim
– Tim, Commented Apr 25, 2014 at 7:04

jonrsharpe · Accepted Answer · 2014-04-25 07:33:25Z

1

Remove your class declaration from Graph.py. When you import all from a file you get all top level objects. In this case it's the Graph class itself, not its methods.

Also you need to pass string 'testcase.txt' not testcase.txt.

edited Apr 25, 2014 at 7:33

jonrsharpe

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answered Apr 25, 2014 at 7:12

Krzysztof Wende

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Comments

jonrsharpe · Accepted Answer · 2014-04-25 07:42:39Z

1

You have multiple problems here:

If you from Graph import * (which is bad practice to start with), you bring Graph into your name space. However, ReadGraph is inside Graph, so to access it you need Graph.ReadGraph.
Having done that, you try to call Dfs.ProcessGraph(testcase.txt,verbose=True). The first argument is interpreted as "pass the txt attribute of the object referenced by name testcase, which doesn't exist. Instead, you mean "testcase.txt" (quoted to make it a string).
Having done all of that, you get e.g. TypeError: unbound method ProcessGraph() must be called with Dfs instance as first argument (got str instance instead). When you call an instance method, the first argument, self by convention, is the instance itself. You have two choices; either a) make e.g. ProcessGraph a @staticmethod, and access it Graph.ReadGraph; or b) move it outside the class, then you can access it directly like you tried to in the first place. As you don't seem to have any class or instance attributes, it's not clear why you are bothering with the classes at all.

What it should probably look like:

import sys 

from Graph import read_graph

def process_graph(file_name, verbose):
  g = read_graph(file_name)

Graph.py module (note absence of class Graph):

def read_graph(file_name):
    ...

(Generally, I suggest you read PEP 8).

edited Apr 25, 2014 at 7:42

answered Apr 25, 2014 at 7:22

jonrsharpe

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6 Comments

Student Over a year ago

When I try: from Graph import read_graph, I get: cannot import name ReadGraph

Student Over a year ago

Yes, when I try compiling Dfs.py I get: ImportError: cannot import name ReadGraph

jonrsharpe Over a year ago

What do you mean "compiling"? If your code in Graph.py doesn't define a class or function ReadGraph at the top level, you can't import it.

Student Over a year ago

When I run the module (press F5). My code in Graph.py has a class called Graph and inside the class has a function called ReadGraph.

jonrsharpe Over a year ago

Please read the whole of my answer; you can't from Graph import ReadGraph if ReadGraph is inside the class Graph.

|

toufikovich · Accepted Answer · 2014-04-25 07:59:54Z

0

your code should be : Dfs.ProcessGraph('testcase.txt',verbose=True) and not Dfs.ProcessGraph(testcase.txt,verbose=True)

'testcase.txt' # is a string and should be between quotes

also check if it is in the same directory where your code live else point to it

plus in DFs you should instantiate Graph :

from Graph.Graph import *
g = Graph()
grf = g.ReadGraph('filename')

EDIT: to be more precise

in Graph module:

class Graph(object):
    def __init__(self):
        pass # for the example now

    def read_graph(self, file_name):
        return file_name

in Dfs Module:

from Graph import *
class Dfs(object):
    def __init__(self):
        pass # for the example now

    def ProcessGraph(file_name, verbose):
        g  = Graph()
        file_name = Graph.read_graph(file_name)

edited Apr 25, 2014 at 7:59

answered Apr 25, 2014 at 7:22

toufikovich

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1 Comment

jonrsharpe Over a year ago

g.ReadGraph('filename') won't work without adding the self argument or @staticmethod decorator.

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