Python Access Variables Outside of Function

Question

Thanks in advance for looking @ this question:

I'm attempting to parse a CSV file, and return the values of certain fields. The code runs perfectly when inline as a script, but when I try to create a function to be accessible by other modules w/in my app, I run into an problem with the variables (keys/values) that I'm pulling from the csv file.

Code to parse CSV (parseCsv.py):

groups =[]
enterprise = []
workinglist = []

def parse_csv(filename):
  quote_char = '"'
  delimiter = ','
  csv_to_parse = open(filename, 'rb')
  csv_reader = csv.DictReader(csv_to_parse, fieldnames=[], restkey='undefined-fieldnames', delimiter=delimiter, quotechar=quote_char)
  current_row = 0
  for row in csv_reader:
    current_row +=1
    if current_row == 1:
      csv_reader.fieldnames = row['undefined-fieldnames']
      continue
    groups.append(row['groupid'])
    enterprise.append(row['enterprise'])
    workinglist.append(row)

I've tried using the global parameter for groups, enterprise, and workinglist; and also tried adding the return groups, return workinglist, return enterprise

Regardless of the syntax, I cannot access the groups, enterprise, or workinglist variables outside of this function. I need to manipulate these results in other parts of my app. If I add print groups within the function, it acts correctly, but from outside the function I end up with a []. I've also tried to make the parse_csv a method of a class, adding a self and an init, with no success.

For reference I'm calling this from another file using parse_csv(csvfilename)It imports the file and reads it correctly.

I'm sure this is something very simple and very quick that I'm missing, but having stared at this so long, I just can't see it, any help would be GREATLY appreciated!

to ease the identification of your issue, please remove all unrelated code until you have a minimal example that reproduces the issue. (typically repl.it/UAZ with the output). As it is, your code may depend on external files such as csv content, which prevent anyone from reproducing your issue. — njzk2
– njzk2, Commented Jun 12, 2014 at 18:34

Pavel · Accepted Answer · 2014-06-12 18:42:39Z

3

you should pass the lists as arguments to the function so that they can be modified. here's how it works:

foo = []

def f(arg):
  arg.append(1)
  arg.append(2)

f(foo)
print foo # output: [1, 2]

this works because the lists are mutable and you pass them by reference.

so you need to implement your function as follows:

def parse_csv(filename, gr, ent, work):
  ...
  gr.append(123)
  work.append(row)
  ...

then you can call it from every file like this:

groups      = []
enterprise  = []
workinglist = []

parse_csv(filename, groups, enterprise, workinglist)

print groups # should contain the data read from CSV

answered Jun 12, 2014 at 18:42

Pavel

7,6022 gold badges33 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

dirtyonekanobi Over a year ago

that worked perfect!! Thank you very much. I can't upvote you until I get a few more points, but I definitely will once I have the opportunity!

Collectives™ on Stack Overflow

Python Access Variables Outside of Function

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related