TypeError: 'NoneType' object is not iterable - Python

Question

I know this question has been asked before but I can't seem to get mine working. Can someone help me out with this?

import sys

class Template:
    def processVariable(self, template, data):
        first = template.find('{{')
        second = template.find('}}')
        second = second + 2
        out = template[first+second]
        assert[out.startswith('{{')]
        out = out.strip('{}')
        rest = template[second:]
        if out in data:
            newstring = data[out]
            return(rest, newstring)
        else:
            print "Invalid Data Passed it"

t = Template()
vars = {
    'name': 'Jane',
    'course': 'CS 1410',
    'adjective': 'shimmering'
}

(rest, out) = t.processVariable('{{name}} is in {{course}}', vars)

This is the error I am getting:

File "template.py", line 28, in <module>
    (rest, out) = t.processVariable('{{name}} is in {{course}}', vars)
TypeError: 'NoneType' object is not iterable

I understand the NoneType but is it because of my for loop or did I just miss something simple? Thanks in advance!

My code will be passed into a field so that my teacher can run a code against it and it will pass or fail. This is what his code will run:

import Candidate

t = Candidate.Template()
vars = {
    'name': 'Jane',
    'course': 'CS 1410',
    'adjective': 'shimmering'
}

(rest, out) = t.processVariable('{{course}} is {{adjective}}', vars)
print 'rest is: [' + rest + ']'
print 'out is : [' + out + ']

what it should return is:

rest is: [ is in {{course}}]
out is : [Jane]

it will return Yes or No if it worked.

Answer 1

There are errors in your code.

This:

out = template[first+second]
assert[out.startswith('{{')]

Should be:

out = template[first:second]
assert out.startswith('{{')

And:

    else:
        print "Invalid Data Passed it"

Should probably be:

    else:
        raise ValueError('Invalid data')

Also this functionality is already in Python:

from string import Template
t = Template('$name is in $course')

vars = {
    'name': 'Jane',
    'course': 'CS 1410',
    'adjective': 'shimmering'
}

print(t.substitute(vars))

Output:

Jane is in CS 1410

Answer 2

You didn't return anything from your else part, and hence your function will by default return None.

Ad of course, you cannot unpack a None into two variables. Try returning a tuple from your else part like this:

if out in data:
    newstring = data[out]
    return (rest, newstring)
else:
    print "Invalid Data Passed it"
    return (None, None)