Python Postgresql Error Handling
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transactions handling¶ Why does psycopg2 leave database sessions "idle in transaction"? Psycopg normally starts a new transaction the psycopg2 error handling first time a query is executed, e.g. calling cursor.execute(), psycopg2.connect example even if the command is a SELECT. The transaction is not closed until an explicit psycopg2 cursor execute commit() or rollback(). If you are writing a long-living program, you should probably make sure to call one of the transaction closing methods
Psycopg2 Connection String
before leaving the connection unused for a long time (which may also be a few seconds, depending on 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. I receive the error current transaction psycopg2 connection timeout is aborted, commands ignored until end of transaction block and can't do anything else! 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: you must run a rollback() before sending new commands to the session (if this seems too harsh, remember that PostgreSQL supports nested transactions using the SAVEPOINT command). 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? Psycopg's connections can't be shared across processes (but are thread safe). 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. Problems with type conversions¶ Why does cursor.execute() raise the exception can't adapt? Psycopg converts
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programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Getting error messages from psycopg2 exceptions up vote 2 down vote favorite 1 This is my first project using psycopg2 extensively. http://initd.org/psycopg/docs/faq.html I'm trying to find a way to extract the psql error message for whenever a connection attempt fails. I've tested the code below will work if all the variables are set correctly, however whenever an error condition occurs (e.g. user chooses a database that doesn't exist), Python will give me the following: I am unable to connect to the database None Traceback (most recent call last): File "./duplicate_finder.py", line 163, in
use with PostgreSQL. One could argue that PostgreSQL as an Open Source database has one of the largest libraries of Application Programmable Interfaces (API) available for various languages. One such language is Python and it happens to be one of my favored languages. I https://wiki.postgresql.org/wiki/Psycopg2_Tutorial use it for almost all hacking that I do. Why? Well to be honest it is because I am not that great of a programmer. I am a database administrator and operating system consultant by trade. Python ensures that the code that I write is readable by other more talented programmers 6 months from when I stopped working on it. Nine times out of ten, when I am using Python, I am using the language to communicate with a PostgreSQL error handling database. My driver of choice when doing so is called Psycopg. Recently Psycopg2 has been under heavy development and is currently in Beta 4. It is said that this will be the last Beta. Like the first release of Pyscopg the driver is designed to be lightweight, fast. The following article discusses how to connect to PostgreSQL with Psycopg2 and also illustrates some of the nice features that come with the driver. The test platform for this article is Psycopg2, Python python postgresql error 2.4, and PostgreSQL 8.1dev. Psycopg2 is a DB API 2.0 compliant PostgreSQL driver that is actively developed. It is designed for multi-threaded applications and manages its own connection pool. Other interesting features of the adapter are that if you are using the PostgreSQL array data type, Psycopg will automatically convert a result using that data type to a Python list. The following discusses specific use of Psycopg. It does not try to implement a lot of Object Orientated goodness but to provide clear and concise syntactical examples of uses the driver with PostgreSQL. Making the initial connection: #!/usr/bin/python2.4 # # Small script to show PostgreSQL and Pyscopg together # import psycopg2 try: conn = psycopg2.connect("dbname='template1' user='dbuser' host='localhost' password='dbpass'") except: print "I am unable to connect to the database" The above will import the adapter and try to connect to the database. If the connection fails a print statement will occur to STDOUT. You could also use the exception to try the connection again with different parameters if you like. The next step is to define a cursor to work with. It is important to note that Python/Psycopg cursors are not cursors as defined by PostgreSQL. They are completely different beasts. cur = conn.cursor() Now that we have the cursor defined we can execute a query. cur.execute("""SELECT datname from pg_database""") When you have executed your query you need to have a list [variable?] to put your results in. rows = cu