Why does the generator expression in `sum(1 for member in self.members if member.membership_status == ...)` cause a SyntaxError, and how can it be fixed?

In Python, the sum() function expects an iterable. When you write sum(1 for member in self.members if member.membership_status == ...), the generator expression is missing parentheses, so the parser treats the for as part of the sum call, leading to a SyntaxError. The correct syntax is sum(1 for member in self.members if member.membership_status == ...) with parentheses around the generator expression, or more idiomatically, sum(1 for member in self.members if member.membership_status in (MembershipStatus.SILVER, MembershipStatus.GOLD)). Alternatively, you can use a list comprehension: sum(1 for member in self.members if member.membership_status in [MembershipStatus.SILVER, MembershipStatus.GOLD]). The key point is that the generator expression must be enclosed in parentheses so that sum receives a single iterable argument. This pattern is common when counting items that satisfy a condition. Complexity is O(n) time and O(1) extra space.