Python & Swift: Loathing Your Tools

Here is a fun way to waste some time: ensure that you have Python 2.7.12 ¹ installed on your Mac via homebrew or whatever, then launch the swift REPL. You can do this now by just typing swift. Your welcome.

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Applications/Xcode.app/Contents/SharedFrameworks/LLDB.framework/Resources/Python/lldb/__init__.py", line 98, in <module>
    import six
ImportError: No module named six
Traceback (most recent call last):
  File "<string>", line 1, in <module>
NameError: name 'run_one_line' is not defined
Traceback (most recent call last):
  File "<string>", line 1, in <module>
NameError: name 'run_one_line' is not defined
Traceback (most recent call last):
  File "<string>", line 1, in <module>
NameError: name 'run_one_line' is not defined

That nonsense will fill your terminal faster than you can even hit Control-D. It could almost be a game — count the number of NameError dialogs, the lower number wins. I call it… NameError golf.

Well what’s going on here? If you go all the way back to the top of what is now the longest terminal session in history — back to when you typed in swift — you will see the first Traceback. Ahh, it appears LLDB runs some Python script when starting the Swift REPL. And somewhere in that file an attempt is made to load the six module.

What the hell is the six module, and why do I care?

The six module — and now I’m just going to quote from the package site — “provides simple utilities for wrapping over differences between Python 2 and Python 3.”

Yes, that’s right. The culprit is a module that makes it easier to write Python 2 code. Ughhhh.

Fixing This “Problem”

The reason I am getting this error message — in case you already haven’t guessed — is because I have Python 2.7.12 installed. It’s from homebrew. I’m fairly sure that I got it back before 2.7.10 and it’s just been updating itself everytime I brew update; brew upgrade.

For reasons which I won’t go into now I have my homebrew Python binary ahead of my macOS default Python binary in the $PATH. I also don’t have the six module installed for that binary. Normally this isn’t a problem for me because I try my damnest to write everything in Python 3.

So, you can solve this problem by doing one of two things:

1. brew uninstall python
2. pip install six

I chose the first option, because it’s time to stop living in the past.