incorrect exception when using `executemany` within transaction

[wrobell]

Please consider this script

import asyncio
import asyncpg

async def upload(data):
    conn = await asyncpg.connect(database='t01')
    async with conn.transaction():
        await conn.executemany('insert into t (t) values ($1)', data)

loop = asyncio.get_event_loop()

data = ([v] for v in range(10))
loop.run_until_complete(upload(data))

If I change the data = ... line to

data = ([x] for v in range(10))

I am getting

...
  File "asyncpg/protocol/protocol.pyx", line 354, in asyncpg.protocol.protocol.BaseProtocol._ensure_clear_state (asyncpg/protocol/protocol.c:59044)
asyncpg.exceptions._base.InterfaceError: cannot perform operation: another operation is in progres

Keeping the erroneous data = ... line and after commenting out the async with conn.transaction() line, I am getting the following exception

  File "asyncpg/protocol/protocol.pyx", line 181, in genexpr (asyncpg/protocol/protocol.c:55322)
  File "test-script.py", line 11, in <genexpr>
    data = ([x] for v in range(10))
NameError: name 'x' is not defined

When running within transaction, the exception should be exactly the same as running without a transaction - the exception shown on the last listing above.