Type dispatch in Python

operation_dispatch.py

k = OperationKernel()

@k.operation("sql", "sql")
def append(l, r):
    if l.engine == r.engine:
        return "UNION ALL statement"
    else:
        raise RetryOperation(["sql", "rows"])

@k.operation("sql", "rows")
def append(l, r):
    return "chained iterators"

local = SQLTable("local")
remote = SQLTable("remote")

# Try to append two local tables
print k.append(local, local)

# Try to append local and a remote table
print k.append(local, remote)