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SqlAlchemy: locking a table using the `get or create` template

I am using the get_or_create pattern similar to the answer to this question:

Does SQLAlchemy have the equivalent of get_or_create Django?

But I am having problems with another thread creating an instance (with the same pk) between "select" and "insert" of the first thread.

Should the get_or_create function lock the table for two queries? What is the best way to implement locking using SqlAlchemy?

I am using postgresql: http://www.postgresql.org/docs/current/static/sql-lock.html

The only sqlalchemy lock function that I see is " for an update , which doesn't seem to be the correct type of lock?"

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, , , , . http://www.sqlalchemy.org/docs/core/connections.html#using-transactions

... ? - python ( ). . , .

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WoLpH , (EdgeInfo - ):

from sqlalchemy import exc

session.begin_nested()
e_info = EdgeInfo(pk_attr_1=pk_attr_1, pk_attr_2=pk_attr_2)
try:
    session.commit()
except exc.IntegrityError:
    session.rollback()
    e_info = EdgeInfo.get((pk_attr_1, pk_attr_2))
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