Alex Pearce

Python and ROOT on OS X

I don’t find myself using ROOT much on my home machine, but when I do there’s usually something broken.

In this case, it was when trying to use PyROOT, a ROOT interface for Python, that this error made my day:

>>> import ROOT
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/root/lib/", line 85, in <module>
import libPyROOT as _root
ImportError: dlopen(/usr/local/root/lib/, 2): Library not loaded: @rpath/
Referenced from: /usr/local/root/lib/
Reason: image not found

This is using the install as documented in a previous post.

The problem is that the library Python loads can’t find another library it needs. To fix this, the DYLD_LIBRARY_PATH variable needs to be set:


This can be executed directly in the shell or placed in a .bashrc-type file.

Caveat 🔗

This solution is not without fault. Namely, whenever one runs a command with sudo, the following warning appears:

dyld: DYLD_ environment variables being ignored because main executable (/usr/bin/sudo) is setuid or setgid

This is a well known issue with OS X 10.8 (Mountain Lion), complete with a bug report.

At least one workaround is available, but for now I put up with the message in the shell I want to use PyROOT in, manually setting DYLD_LIBRARY_PATH when needed.