StopIteration in Python

Question

I encounter a problem while reading functional programming python.

def get_log_lines(log_file): 
    line = read_line(log_file) 
    while True:
        try:
            if complex_condition(line):
                yield line
            line = read_line(log_file)
        except StopIteration:
            raise

A try...except statement is added to surround the read_line . Why not just let read_line throw the StopIteration exception like this:

def get_log_lines(log_file): 
    line = read_line(log_file) 
    while True:
        if complex_condition(line):
            yield line
        line = read_line(log_file)

Answer 1

I don't think there is any reason to keep the try...except there. The re-raise will still carry the same traceback, for example, so the behaviour of the generator is unchanged with it there.

In other words, it is pointless there, perhaps a left-over artefact of a refactoring.

You can simplify the loop even further, removing the redundant first line:

def get_log_lines(log_file): 
    while True:
        line = read_line(log_file) 
        if complex_condition(line):
            yield line

Answer 2

The author was writing an example. While the try...catch block doesn't actually do anything here, he probably included it so that you could SEE how the loop would get broken.