Configure Python develop tool chain

- use pyenv to manage the develop environments
  + install several Python versions (3.7 - 3.10 and 2.7)
  + each version receives its own copies of black, pipenv, and poetry
- add two more virtual environments based off the latest version:
  + "interactive" => default environment optimized for interactive
                     usage with with black, bpython, and ipython
                     (also receives accidental `pip install`s)
  + "utils" => hosts various globally available tools/apps
               (e.g., mackup and youtube-dl)
- add installation and update scripts for the entire tool chain
- set up completions for bash and zsh
- set up convenient aliases
- configure bpython
- configure poetry

.zshrc

@@ -5,6 +5,12 @@
 [[ $- != *i* ]] && return
 
 
+# Check if a command can be found on the $PATH
+_command_exists() {
+    command -v "$1" 1>/dev/null 2>&1
+}
+
+
 
 # Enable Powerlevel10k instant prompt
 if [ -r "${XDG_CACHE_HOME:-$HOME/.cache}/zsh/p10k-instant-prompt-${(%):-%n}.zsh" ]; then
@@ -61,7 +67,10 @@ plugins=(
     dirhistory
     dotenv             # config in ~/.zshenv; `_update_repositories` temporarily disables this
     git-escape-magic
+    invoke             # completions for invoke
     jsontools
+    pip                # completions for pip
+    poetry             # completions for poetry
     z
 )
 
@@ -124,6 +133,21 @@ zstyle ':completion:*:warnings' format 'No matches for: %d'
 zstyle ':completion:*' group-name ''
 
 
+# Enable completions for various tools
+
+# invoke -> see plugins above; alternatively use
+# _command_exists invoke && eval "$(invoke --print-completion-script=zsh)"
+
+_command_exists nox && eval "$(register-python-argcomplete nox)"
+
+# pip -> see plugins above; alternatively use
+# _command_exists pip && eval "$(pip completion --zsh)"
+
+_command_exists pipx && eval "$(register-python-argcomplete pipx)"
+
+# poetry -> see plugins above; no alternative here
+
+
 
 # Define key bindings