Unguarded next inside generatorPTC-W0063

Calls to next() should be inside try-except block.

When the iterator is exhausted, StopIteration exception is raised. When used inside a generator, this can cause unexpected behavior. If not handled, it will propagate out of the generator causing termination. PEP-479 has been accepted to fix this problem. It will modify the behavior of StopIteration in generators.

Each call to next() should be wrapped in a try-except block to explicitly handle StopIteration exceptions.

Bad practice

def get_team_structure(team):
    for team in class:
        students = iter(team)
        # StopIteration exception will be raised if team doesn't have members.
        leader = next(students)
        members = [m for m in students]
        yield leader, members

def print_teams(teams):
    for leader, members in get_team_structure(teams):
        print("Leader: "leader)
        for member in members:
            print(member)

Recommended:

def get_team_structure(team):
    for team in class:
        # StopIteration exception will be raised if team has no members.
        students = iter(team)
        # Added `try` block, to guard against the exception
        try:
            leader = next(students)
        except StopIteration:
            # team has no members, skip it
            continue

        members = [m for m in students]
        yield leader, members

def print_teams(teams):
    for leader, members in get_team_structure(teams):
        print("Leader: "leader)
        for member in members:
            print(member)
    ...