Question

SO I am reading a text file which has 2 columnn

 foo, bar

SO i did something like

for each_line in f:
   each_line = each_line.split(',')
   foo = int(each_line[0])
   bar = int(each_line[1]
   foobar = FooBar(foo,bar)
   foobar_list.append(foobar)

Now, sometimes either foo or bar is blank.. hence cant be typecasted to int..
Is there a way that if something where foo or bar is empty I can just skip this feature

(doesnt get appended to foodbar) but then the loops stills keeps on going ??

Answer 1

There are a couple of places this could possibly fail, either if each_line doesn’t have enough commas, or if either value was not a number (say, an empty string). In each case, you can catch the error and use continue to skip to the next item in f:

for each_line in f:
   try:
       foo_line, bar_line = each_line.split(',')
   except ValueError:
       # "Too many/few values to unpack" meaning wrong number of commas!
       continue
   try:
       foo, bar = int(foo_line), int(bar_line)
   except ValueError:
       # "invalid literal for int()" meaning it wasn't digits
       continue
   foobar = FooBar(foo,bar)
   foobar_list.append(foobar)

I’ve broken this down into two, separate exception handlers because there are two different ways for it to fail. You actually could fold it up like:

for each_line in f:
   try:
       foo_line, bar_line = each_line.split(',')
       foo, bar = int(foo_line), int(bar_line)
   except ValueError:
       # there was invalid input.
       continue
   foobar = FooBar(foo,bar)
   foobar_list.append(foobar)

Since it’s the same exception and they happen close together. Personally, i prefer the former to make it really clear that there are two kinds of errors. What you should NOT do is:

# !!! BAD !!!
for each_line in f:
    try:
        each_line = each_line.split(',')
        foo = int(each_line[0])
        bar = int(each_line[1]
        foobar = FooBar(foo,bar)
        foobar_list.append(foobar)
    except ValueError:
        continue

because FooBar() or even foobar_list.append() could fail, but the exception handler can swallow it; Always make the try: suite in yoru exception handlers as small as possible so that they only catch one error, and where the error is is easy to find.