Homebrew installations have PYENV_ROOT set to `~/.pyenv`, while the
actual completion file resides in /home/linuxbrew/.linuxbrew/Cellar/pyenv/2.4.23/completions/pyenv.zsh
Thus, if you try to use `$PYENV_ROOT/completions/pyenv.${shell}`, the
completions file will not be found, since you are pointing to:
`~/.pyenv/completions/pyenv.zsh`
when the actual location is:
`/home/linuxbrew/.linuxbrew/Cellar/pyenv/2.4.23/completions/pyenv.zsh`
This problem is resolved by using the parent folder of the currently
executing file:
`/home/linuxbrew/.linuxbrew/Cellar/pyenv/2.4.23/libexec/pyenv-init`
which is
`/home/linuxbrew/.linuxbrew/Cellar/pyenv/2.4.23`
And then go to completions from there.
I don't like the fact that homebrew installations store some things in
`/home/linuxbrew/.linuxbrew/Cellar/pyenv/2.4.23/libexec/pyenv-init`
while stuff like `shims` and python versions are stored in `~/.pyenv`, but
that's how it currently is.
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