Python Code Structure

Question

I have some Python 3.4 code I have written that does execute correctly but when using different IDE's to help me find errors I get a variable referenced before assignment error in this code snippet:

if os.path.isfile(o.options_file): # Make sure this really is a file.
 options = (csv.reader(open(o.options_file), delimiter='\t'))
else:
 exit("Options_File Not Found. Check File Name and Path.")
count = 0
for line in options:
 count += 1

It is the options variable that is throwing the error. Can this be ignored or should I assign a Null value to options?

• Terry Jan Reedy: A code checker should give you an ignorable warning here, not an error. A false error claim is an error. On the other hand, Martijn's 'bail first on error' solution is a pretty good practice in general..

Answer 1

You could just invert the test:

if not os.path.isfile(o.options_file): # Make sure this really is a file.
 exit("Options_File Not Found. Check File Name and Path.")
options = (csv.reader(open(o.options_file), delimiter='\t'))
count = 0
for line in options:
 count += 1

This makes it far clearer, both to code linting tools and other developers, that the rest of the code won't run if the file doesn't exist.