How to pass a string into a function in Python

Question

Being new to Python, but still unescapable, I'm stuck on this problem. What I'm trying to do is pass a string into the function to get it extended.

Here is what I have:

def replace(source, destination):
    local_source = src_tree.find("source")
    local_destination = dest_tree.find("destination")
    local_destination.extend(local_source)

replace(source=".//animal-list/dog", destination=".//animal-list/dog")

This piece of code will work if I don't place it in a function. But because I have hundreds of these "expend" that I have to achieve, why not the good o' function calling.

Originally I have this, and it works as what I need:

src = src_tree.find('.//animal-list/dog')
dest = dest_tree.find('.//animal-list/dog')
dest.extend(src)

And what that would do is "replace" the dest dog with src dog. Works perfect, but I'm trying to make it into a function for easier use.

My question would be, what am I doing wrong in the function? Since it is tossing up a exception.

Traceback (most recent call last):
  File "test.py", line 28, in <module>
    replace(source=".//animal-list/dog", destination=".//animal-list/dog")
  File "test.py", line 13, in replace
    local_destination.extend(local_source)
AttributeError: 'NoneType' object has no attribute 'extend'

"source" and "destination" shouldn’t be in quotes if you want to pass their values. — Ry-
– Ry- ♦, Commented Jan 17, 2014 at 3:36
Strange how I thought I tried that and still gave me exception. I might be wrong, been going at this program (not particularly this problem) for over 12 hours now. (Rushing for Wednesday release). Problem is, I speak no Python before Wednesday. — misterbear
– misterbear, Commented Jan 17, 2014 at 3:46
It might have been a different exception. I think I just been in front of the computer for far too long. — misterbear
– misterbear, Commented Jan 17, 2014 at 4:48

mojo · Accepted Answer · 2014-01-17 03:36:31Z

2

You've quoted things that should be variables (source and destination). It should be:

def replace(source, destination):
    local_source = src_tree.find(source)
    local_destination = dest_tree.find(destination)
    local_destination.extend(local_source)

answered Jan 17, 2014 at 3:36

mojo

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John La Rooy · Accepted Answer · 2014-01-17 03:36:55Z

1

Here you are passing a literal string, instead of the variable

local_destination = dest_tree.find("destination")

Perhaps dest_tree.find is returning None because of that. Try this instead

local_destination = dest_tree.find(destination)

And likewise where you have used "source" instead of source

answered Jan 17, 2014 at 3:36

John La Rooy

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