将 try/except 应用于多个 Python class 定义

Question

is there a way to apply try/except logic to multiple class definitions without a try/except in every definition?

For example, instead of:

def test_table(tablename):
    return Table(tablename, db.metadata, Column('id', Integer, primary_key=True))

class User(db.Model):
    try:
        __table__ = db.metadata.tables['user']
        __bind_key__ = 'secondary'
        # More attrs...
    except KeyError:
        __table__ = test_table('user')


class Policy(db.Model):
    try:
        __table__ = db.metadata.tables['policy']
        __bind_key__ = 'secondary'
        # More attrs...
    except KeyError:
        __table__ = test_table('policy')

I could apply logic with a decorator like:

@if_no_metadata_use_default('user')
class User(db.Model):
        __table__ = db.metadata.tables['user']
        __bind_key__ = 'secondary'
        # More attrs...

@if_no_metadata_use_default('policy')
class Policy(db.Model):
    __table__ = db.metadata.tables['policy']
    __bind_key__ = 'secondary'
    # More attrs...

Answer 1

This might not be a good practice in general since it really decreases your code readablity, but you can create an exception_wrapper decorator like this:

def exception_wrapper(func):
    def run(exception, on_exception, *args, **kwargs):
        try:
            return func(*args, **kwargs)
        except exception:
            on_exception()

    return run


def on_exception():
    pass


@exception_wrapper
def f(a, b):
    if a < b:
        raise NotImplementedError
    return a + b


print(f(NotImplementedError, on_exception, 10, 2))

Again, I'm against using this kind of wrappers for exceptions since they will make your life harder in the long run, but it's up to you!