Good practice for branching on try/except

Question

Suppose my python code branches based on the result of a try/except as follows:

def(x):
    no_errors = False
    try:
        y = f(x)
        no_errors = True
    except ZError:
        no_errors = False
    if no_errors:
        do_stuff(y)
    else:
        do_other_stuff(x)

My linter warns that y may be undefined. Is this poor practice? What is the recommended fix?

Answer 1

Typically, you wouldn't have code structured like this. You'd have else and/or finally clauses in the try statement.

def f(x):
    try:
        y = f(x)
    except ZError:
        do_other_stuff(x)
    else:
        do_stuff(y)

Answer 2

y will be undefined if y = f(x) throws any kind of exception that is not a ZError . Technically, the variable no_errors really means "no ZError s". You could handle this more elegantly using an else or finally block to define y .

For example:

def(x):
    no_errors = false
    try:
        y = f(x)
        no_errors = True
    except ZError:
        no_errors = False
    finally:
        y = some_default
    if no_errors:
        do_stuff(y)
    else:
        do_other_stuff(x)

Also, the bool is not needed, since you can simply leverage the conditional nature of the try / except blocks (see chepner's answer)