Question

I have been here for a couple of months learning python from examples, but the time has come to ask one for myself.

I am currently working on a script here at work that scrapes the job queue from a website & sends a notification if a certain condition exists.

The hard part is out of the way & I have the results being split into nested lists, but when I try & search for a specific condition I get an error if it doesn’t exist.

customers = [['00:00:02', 'S3'], ['00:00:46', 'S2']]

[item for item in customers if 'S2' in item[1]]
print('%s %s') % (item[1], item[0])

The condition above works well if there is a ‘S2’ condition, but if there isn’t (because the page im scraping from may not have one) I get an error:

UnboundLocalError: local variable 'item' referenced before assignment

This is probably a very basic question but how can I stop this error from occurring?

Answer 1

In python 2.x, the variables used inside of list comprehensions (here, item) leaks out of the list comprehension into the surrounding scope. Using it afterwards is not typically a good idea, or clear code. Try something like this:

filtered_list = [item for item in customers if 'S2' in item[1]]
for item in filtered_list:
    print('%s %s') % (item[1], item[0])