code passenger_wsgi python

Question

Can someone explain why this code shows a new version of Python on Dreamhost ?

import sys,os
# Force Passenger to run our virtualenv python
INTERP = "/home/site/env/bin/python"
if sys.executable != INTERP: os.execl(INTERP, INTERP, *sys.argv)
def application(environ, start_response):
    start_response('200 OK', [('Content-type', 'text/plain')])
    return ["Hello, world!" + sys.version]

While this code shows an old version :

#!/home/site/env/bin/python
import sys
def application(environ, start_response):
    start_response('200 OK', [('Content-type', 'text/plain')])
    return ["Hello, world!" + sys.version]

Answer 1

If you throw some debugging code in passenger_wsgi.py to write out a log file:

x = open(os.path.expanduser('~/log.log'), 'w')
x.write(repr(sys.argv))
x.close()

and then examine ~/log.log, then you’ll find that the python process that loads passenger_wsgi.py is started by running /dh/passenger/lib/phusion_passenger/wsgi/request_handler.py.

The first line of /dh/passenger/lib/phusion_passenger/wsgi/request_handler.py is

#!/usr/bin/env python

and it loads passenger_wsgi.py by calling

app_module = imp.load_source('passenger_wsgi', 'passenger_wsgi.py')

Since passenger_wsgi.py is loaded as a Python module, the #!/home/site/env/bin/python line at the start of your second passenger_wsgi.py file is treated simply as a Python comment and ignored. The default /usr/bin/python is used instead.

The recommended fix for this is exactly what your first passenger_wsgi.py does: execl the version of Python you actually want. I usually compile Python 2.7 in the shell user’s home directory and use that.

PS: If you’re curious I have some notes about setting up Django on Dreamhost so that you can do continuous deployment…