Re using libpq floats and binary data
Here are a few gotchas you may encounter using psycopg2. Feel free to suggest new entries! Psycopg normally starts a new transaction the first time a query is executed, e. The transaction is not closed until an explicit commit or rollback. If re using libpq floats and binary data are writing a long-living program, you should probably make sure to call one of the transaction closing methods before leaving the connection unused for a long time which may also be a few seconds, depending re using libpq floats and binary data the concurrency level in your database.
Alternatively you can use a connection in autocommit mode to avoid a new transaction to be started at the first command. All Python objects are converted by Psycopg in their SQL representation, so they get passed to the query as strings. See Passing parameters to SQL queries. Psycopg always require positional arguments to be passed as a sequence, even when the query takes a single parameter. And remember that to make a single item tuple in Python you need a comma!
See Unicode handling for the gory details. If you find psycopg2. See JSON adaptation for further details. Automatic conversion of jsonb values is supported from Psycopg release 2.
For previous versions you can register the json typecaster on the jsonb oids which are known and not suppsed to change in future PostgreSQL versions:. The arguments in the execute methods can only represent data to pass to the query: If you want to build a query dynamically you can use the objects exposed by the psycopg2.
The problem is solved in Psycopg 2. For previous Psycopg releases, three options to solve the problem are:. Normally the interactive shell becomes unresponsive to Ctrl-C when running a query.
Starting from psycopg 2. For previous versions, you can use this implementation. Fast-forward several years, if the message reports undefined symbol: Re using libpq floats and binary data index modules next previous Psycopg 2. There was a problem in the previous command to the database, which resulted in an error. The database will not recover automatically from this condition: Why do I get the error current transaction is aborted, commands ignored until end of transaction block when I use multiprocessing or any other forking system and not when use threading?
If you are forking the Python process make sure to create a new connection in each forked child. See Thread and process safety for further informations. Psycopg converts Python objects in a SQL string representation by looking at the object class. The exception is raised when you are trying to pass as query parameter an object for which there is no adapter registered for its class. This doesn't work cur. Cursors are lightweight objects and creating lots of them should not pose any kind of problem.
But note that cursors used to fetch result sets will cache the data and use memory in proportion to the result set size. Our suggestion is to almost always create a new cursor and dispose old ones as soon as the data is not required anymore call close on them.
When should I save and re-use a connection as opposed to creating a new one as needed? Creating a connection can be slow think of SSL over TCP so the best practice is to create a single connection and keep it open as long as required. What are the advantages or disadvantages of using named cursors?
The only disadvantages is that re using libpq floats and binary data use up resources on the server and that there is a little overhead because a at least two queries one to create the cursor and one to fetch the initial result set are issued to the backend. The advantage is that data is fetched one chunk at a time: How do I interrupt a long-running query in an interactive shell?
No such file or directory. What am I missing? You need to install a Python development package: You need to install the re using libpq floats and binary data version of the libpq: Table Of Contents Frequently Asked Questions Problems with transactions handling Problems with type conversions Best practices Problems compiling and deploying psycopg2 Previous topic psycopg2.
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