Debugging (displaying) SQL command sent to the db by SQLAlchemy

Question

I have an ORM class called Person, which wraps around a person table:

After setting up the connection to the db etc, I run the statement:

people = session.query(Person).all() 

The person table does not contain any data (as yet), so when I print the variable people, I get an empty list.

I renamed the table referred to in my ORM class People, to people_foo (which does not exist).

I then run the script again. I was surprised that no exception was thrown when attempting to access a table that does not exist.

I therefore have the following 2 questions:

1. How may I setup SQLAlchemy so that it propagates db errors back to the script?
2. How may I view (i.e. print) the SQL that is being sent to the db engine?

If it helps, I am using PostgreSQL.

[Edit]

I am writing a package. In my __main__.py script, I have the following code (shortened here):

### __main__.py import common # imports logging and defines logging setup funcs etc  logger = logging.getLogger(__name__)   def main():         parser = OptionParser(usage="%prog [options] <commands>",                           version="%prog 1.0")      commands = OptionGroup(parser, "commands")      parser.add_option(         "-l",         "--logfile",         dest="logfile",         metavar="FILE",         help="log to FILE. if not set, no logging will be done"     )      parser.add_option(         "--level",         dest="loglevel",         metavar="LOG LEVEL",         help="Debug level. if not set, level will default to low"     )      # Set defaults if not specified     if not options.loglevel:         loglevel = 1     else:         loglevel = options.loglevel      if not options.logfile:         logfilename = 'datafeed.log'     else:         logfilename = options.logfile      common.setup_logger(False, logfilename, loglevel)          # and so on ...            #### dbfuncs.py   import logging      # not sure how to 'bind' to the logger in __main__.py     logging.getLogger('sqlalchemy.engine').setLevel(logging.INFO)      engine = create_engine('postgres://postgres:pwd@localhost:port/dbname', echo=True) 

[Edit2]

Common module sets the logger up correctly, and I can use the logger in my other modules that import common.

However in dbfuncs module, I am getting the following error/warning:

No handlers could be found for logger "sqlalchemy.engine.base.Engine

Answer 1

In addition to echo parameter of create_engine() there is a more flexible way: configuring logging to echo engine statements:

import logging logging.basicConfig() logging.getLogger('sqlalchemy.engine').setLevel(logging.INFO) 

See Configuring Logging section of documentation for more information.

Answer 2

You can see the SQL statements being sent to the DB by passing echo=True when the engine instance is created (usually using the create_engine() or engine_from_config() call in your code).

For example:

engine = sqlalchemy.create_engine('postgres://foo/bar', echo=True) 

By default, logged statements go to stdout.