Postgres.app and psycopg2 on OS X

October 13, 2013 at 10:17 pm

Attention

Turns out that system library changes also affect the compilation process of psycopg2. Overall, not their fault but definitely something to keep in mind. The original article is below.

I had a lot of fun today after upgrading psycopg2 to 2.5.1. I was playing around with SQLAlchemy so I ran the normal commands for getting a Postgres database up and running.

$ virtualenv venv
$ source venv/bin/activate
$ pip install psycopg2
$ python
>>> from models.py import get_engine
>>> e = get_engine()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "models.py", line 11, in get_engine
    engine = create_engine("postgres://localhost/leadgen", echo=True)
  File "/Users/josh/Dropbox/Projects/sqla/venv/lib/python2.7/site-packages/sqlalchemy/engine/__init__.py", line 332, in create_engine
    return strategy.create(*args, **kwargs)
  File "/Users/josh/Dropbox/Projects/sqla/venv/lib/python2.7/site-packages/sqlalchemy/engine/strategies.py", line 64, in create
    dbapi = dialect_cls.dbapi(**dbapi_args)
  File "/Users/josh/Dropbox/Projects/sqla/venv/lib/python2.7/site-packages/sqlalchemy/dialects/postgresql/psycopg2.py", line 368, in dbapi
    import psycopg2
  File "/Users/josh/Dropbox/Projects/sqla/venv/lib/python2.7/site-packages/psycopg2/__init__.py", line 67, in <module>
    from psycopg2._psycopg import BINARY, NUMBER, STRING, DATETIME, ROWID
ImportError: dlopen(/Users/josh/Dropbox/Projects/sqla/venv/lib/python2.7/site-packages/psycopg2/_psycopg.so, 2): Library not loaded: @loader_path/../lib/libssl.1.0.0.dylib
  Referenced from: /Users/josh/Dropbox/Projects/sqla/venv/lib/python2.7/site-packages/psycopg2/_psycopg.so
  Reason: image not found

What the hell is that?!?

First thing I did is jump into some Google searches. Ironically the first result hit was a StackOverflow question that ultimately solved my issue but I wasn’t settling at the time for an easy solution. This had worked seconds before on another application. Why wasn’t it working now?

I jumped over to another Django (1.4) application I had running and tried upgrading psycopg2. Upgrade and build worked fine, but now I had the same error as with the SQLAlchemy application. Looked like psycopg2 version was the culprit here. I tried downgrading to the previous version of psycopg2 (2.4.5). Now the same damn error with the previous version. This can’t be good.

Another project I had (running Django 1.5) had the same (old, 2.4.5) version of psycopg2. Directly copying it to the existing (Django 1.4) project worked fine. It looks like psycopg2==2.4.5 had been updated at some point and this is why fresh installs were failing out with this Reason: image not found error.

Finally I was at the point where I thought soft linking libraries on my system was a decent way to solve the problem. Postgres.app by the nice guys at Heroku is where all my PostgreSQL related stuff lives. The path for the two required dylibs is /Applications/Postgres.app/Contents/MacOS/lib/libssl.1.0.0.dylib and /Applications/Postgres.app/Contents/MacOS/lib/libcrypto.1.0.0.dylib. Both of these need to be linked into /usr/local. There is already a linked file (libssl.dylib and libcrypto.dylib) in that folder on my system that point to libssl.0.9.8.dylib and libcrypto.0.9.8.dylib respectively. I wouldn’t recommend changing these so I simply softlinked the new 1.0.0 versions into that folder. These commands require sudo for obvious reasons.

cd /usr/lib
sudo ln -s /Applications/Postgres.app/Contents/MacOS/lib/libssl.1.0.0.dylib libssl.1.0.0.dylib
sudo ln -s /Applications/Postgres.app/Contents/MacOS/lib/libcrypto.1.0.0.dylib libcrypto.1.0.0.dylib

Flipping back to my Django 1.4 app I can confirm it works as expected. My SQLAlchemy application works too now.

Other points for troubleshooting

The error here is pretty explicit. Something was expected that could not be found. Google is your friend, and often some of the first results are OK. No need to feel that a spontaneous problem shouldn’t be resolved by a little softlinking.

That said, it’s important to realize that when you push a package at a version number it should be frozen. I should be able to bring down the exact same code by specifying what version number of a package. Have you changed or improved something? Great! Time to increment that minor version number.

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October 2013

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