Python: How to import variables from another file by passing arguments

Question

Trying to build code-list independent from main file

#### expense_codelist.py ####
def thelist(filename_list):
    fn_type = filename_list.split('-')
    pay_method_var = fn_type[1]
    if fn_type[0] == 'Chase':
        pay_method_val = 'Credit Card'
        card_name == 'Chase'
        proceed = 'Y'
    if fn_type[0] == 'Expenses':
        pay_method_val = 'Debit Card'
        card_name = 'Bancontact'
        proceed = 'Y'
        return
    if fn_type[0] == 'ING Credit Card':
        pay_method_val = 'Credit Card'
        card_name = 'ING'
        proceed = 'Y'
    if fn_type[0] == 'Capital One':
        pay_method_val = 'Credit Card'
        card_name = 'Capital One'
        proceed = 'Y'

I want to use the variables pay_method_val, card_name, proceed to be returned to the main script. What I tried is below:

#### process.py ####
import expense_codelist
print expense_codelist.thelist(incsvfn)proceed

I am getting the below Error:

print expense_codelist.thelist(incsvfn).proceed
AttributeError: 'NoneType' object has no attribute 'proceed'

Answer 1

You could use the collections module and put

TheList = collections.namedtuple('TheList', 'pay_method_val, card_name, proceed')
return TheList(pay_method_val, card_name, proceed)

a the end of your function, but this feels like a bit of a hack.

What you probably want is a class which stores the data, and would be written like this:

class TheList(object):
    def __init__(self, filename_list):
        fn_type = filename_list.split('-')
        self.pay_method_var = fn_type[1]
        if fn_type[0] == 'Chase':
            self.pay_method_val = 'Credit Card'
            self.card_name == 'Chase'
            self.proceed = 'Y'
        elif fn_type[0] == 'Expenses':
            self.pay_method_val = 'Debit Card'
            self.card_name = 'Bancontact'
            self.proceed = 'Y'
        elif fn_type[0] == 'ING Credit Card':
            self.pay_method_val = 'Credit Card'
            self.card_name = 'ING'
            self.proceed = 'Y'
        elif fn_type[0] == 'Capital One':
            self.pay_method_val = 'Credit Card'
            self.card_name = 'Capital One'
            self.proceed = 'Y'

which would be called like so:

import expense_codelist
thelist = expense_codelist.TheList(incsvfn)
print thelist.proceed

Answer 2

If you just want the values of those variables (and not an object containing them), you can simply return them:

#### expense_codelist.py ####
def thelist(filename_list):
    fn_type = filename_list.split('-')
    pay_method_var = fn_type[1]
    if fn_type[0] == 'Chase':
        pay_method_val = 'Credit Card'
        card_name == 'Chase'
        proceed = 'Y'
    elif fn_type[0] == 'Expenses':
        pay_method_val = 'Debit Card'
        card_name = 'Bancontact'
        proceed = 'Y'
        return
    elif fn_type[0] == 'ING Credit Card':
        pay_method_val = 'Credit Card'
        card_name = 'ING'
        proceed = 'Y'
    elif fn_type[0] == 'Capital One':
        pay_method_val = 'Credit Card'
        card_name = 'Capital One'
        proceed = 'Y'
    else:
        raise ValueError("Card type not recognized")
    return pay_method_var, pay_method_val, card_name, proceed

And in your other file just save them to local variables:

#### process.py ####
import expense_codelist
pay_method_var, pay_method_val, card_name, proceed = expense_codelist.thelist(incsvfn)
print proceed

I also made your if chain an if..elif..else chain. Your strings are mutually exclusive (and there should be code handling the case where the card type is something unexpected).