Lance Collins Lance Collins - 3 months ago 7
Python Question

function is not defined error in Python

I am trying to define a basic function in python but I always get the following error when I run a simple test program;

>>> pyth_test(1, 2)

Traceback (most recent call last):
File "<pyshell#2>", line 1, in <module>
pyth_test(1, 2)
NameError: name 'pyth_test' is not defined


Here is the code I am using for this function;

def pyth_test (x1, x2):
print x1 + x2


UPDATE: I have the script called pyth.py open, and then I am typing in pyth_test(1,2) in the interpreter when it gives the error.

Thanks for the help. (I apologize for the basic question, I've never programmed before and am trying to learn Python as a hobby)




import sys
sys.path.append ('/Users/clanc/Documents/Development/')
import test


printline()



## (the function printline in the test.py file
##def printline():
## print "I am working"

Answer

Yes, but in what file is pyth_test's definition declared in? Is it also located before it's called?

Edit:

To put it into perspective, create a file called test.py with the following contents:

def pyth_test (x1, x2):
    print x1 + x2

pyth_test(1,2)

Now run the following command:

python test.py

You should see the output you desire. Now if you are in an interactive session, it should go like this:

>>> def pyth_test (x1, x2):
...     print x1 + x2
... 
>>> pyth_test(1,2)
3
>>> 

I hope this explains how the declaration works.


To give you an idea of how the layout works, we'll create a few files. Create a new empty folder to keep things clean with the following:

myfunction.py

def pyth_test (x1, x2):
    print x1 + x2 

program.py

#!/usr/bin/python

# Our function is pulled in here
from myfunction import pyth_test

pyth_test(1,2)

Now if you run:

python program.py

It will print out 3. Now to explain what went wrong, let's modify our program this way:

# Python: Huh? where's pyth_test?
# You say it's down there, but I haven't gotten there yet!
pyth_test(1,2)

# Our function is pulled in here
from myfunction import pyth_test

Now let's see what happens:

$ python program.py 
Traceback (most recent call last):
  File "program.py", line 3, in <module>
    pyth_test(1,2)
NameError: name 'pyth_test' is not defined

As noted, python cannot find the module for the reasons outlined above. For that reason, you should keep your declarations at top.

Now then, if we run the interactive python session:

>>> from myfunction import pyth_test
>>> pyth_test(1,2)
3

The same process applies. Now, package importing isn't all that simple, so I recommend you look into how modules work with Python. I hope this helps and good luck with your learnings!