Caveats

Python

LLDB has a powerful scripting interface which is accessible through Python. Python is available either from within LLDB through a (interactive) script interpreter, or as a Python module which you can import from the Python interpreter.

To make this possible, LLDB links against the Python shared library. Linking against Python comes with some constraints to be aware of.

  1. It is not possible to build and link LLDB against a Python 3 library and use it from Python 2 and vice versa.
  2. It is not possible to build and link LLDB against one distribution on Python and use it through a interpreter coming from another distribution. For example, on macOS, if you build and link against Python from python.org, you cannot import the lldb module from the Python interpreter installed with Homebrew.
  3. To use third party Python packages from inside LLDB, you need to install them using a utility (such as pip) from the same Python distribution as the one used to build and link LLDB.

The previous considerations are especially important during development, but apply to binary distributions of LLDB as well.

LLDB in Xcode on macOS

Users of lldb in Xcode on macOS commonly run into these issues when they install Python, often unknowingly as a dependency pulled in by Homebrew or other package managers. The problem is the symlinks that get created in /usr/local/bin, which comes before /usr/bin in your path. You can use which python3 to check to what it resolves.

To be sure you use the Python that matches with the lldb in Xcode use xcrun or use the absolute path to the shims in /usr/bin.

$ xcrun python3
$ /usr/bin/python3

Similarly, to install packages and be able to use them from within lldb, you’ll need to install them with the matching pip3.

$ xcrun pip3
$ /usr/bin/pip3

The same is true for Python 2. Although Python 2 comes with the operating system rather than Xcode, you can still use xcrun to launch the system variant.

$ xcrun python
$ /usr/bin/python

Keep in mind that Python 2 is deprecated and no longer maintained. Future versions of macOS will not include Python 2.7.