Zsh completion for pip (a tool for installing and managing Python packages), to be added to Zsh soonish.

_pip.zsh

#compdef -P pip[0-9.]#
#
# Completion script for pip (http://pypi.python.org/pypi/pip).
#
# Taken from https://github.com/zsh-users/zsh-completions/commit/890f3701
# (where it got removed).  Original source:
# https://github.com/technolize/zsh-completion-funcs.
#
# Currently maintained in https://gist.github.com/blueyed/54a257c411310a28805a.

# Setup $python, based on pip version from word[1].
# Must get done early, otherwise $words might have been changed already.
local python pip
pip=${words[1]}
python=${${pip}/pip/python}
[[ $python == $pip ]] && python=python


# The index(es) to use.  The simple index only provides a full list, while
# the xmlrpc index can be queried by "last updated in".
# This should be probably made configurable through zstyle and then be used
# in the cache name.
# For the xmlrpc index, the "days" could be made configurable
typeset -a ZSH_PIP_INDEXES ZSH_PIP_XMLRPC_INDEXES

# Enabling this would additionally use the simple PyPI index, which does not
# support limiting by date.
# ZSH_PIP_INDEXES=(https://pypi.python.org/simple/)

# The XMLRPC index, which supports filtering by "last updated since".
ZSH_PIP_XMLRPC_INDEXES=(https://pypi.python.org/pypi)
# Using packages updated in the last year results in ~26798 packages currently.
local ZSH_PIP_XMLRPC_INDEX_DAYS=365


# Get all packages from (remote) indexes.
_pip_all() {
  _pip_set_cache_policy

  if ( (( $+__zsh_pip_all_pkgs )) && ! _cache_invalid pip_allpkgs ) \
      || _retrieve_cache pip_allpkgs; then
    return
  fi

  typeset -a -g __zsh_pip_all_pkgs
  if zstyle -T ":completion:${curcontext}:" remote-access; then
    typeset -a new_zsh_all_pkgs
    local ts_xmlrpc_start
    if zmodload -F zsh/datetime +p:EPOCHSECONDS 2>/dev/null; then
      ts_xmlrpc_start=$((EPOCHSECONDS - (86400 * ZSH_PIP_XMLRPC_INDEX_DAYS)))
    else
      ts_xmlrpc_start=$(date +%s -d @$(($(date +%s) - (86400 * ZSH_PIP_XMLRPC_INDEX_DAYS))))
    fi

    # Build XMLPC request to pypi.python.org to get a list of packages updated
    # in the last year.  This is meant to reduce the number of packages.
    local xml_req="<?xml version='1.0'?><methodCall><methodName>updated_releases</methodName><params><param><value><int>${ts_xmlrpc_start}</int></value></param></params></methodCall>"

    # TODO: Standard error is not redirected
    for xmlrpc_index in $ZSH_PIP_XMLRPC_INDEXES; do
      new_zsh_all_pkgs+=($(_call_program fetch-all-xml "echo ${(qqqq)xml_req} \
        | curl -s --max-time 30 -d @- -H \"Content-Type: text/xml\" $xmlrpc_index \
        | sed -n '/^<value><string>/p' | sed -n '1~2 s/^<value><string>//p' | sed -n 's/<\/string><\/value>$//p' \
        | tr '\n' ' '") )
    done

    for index in $ZSH_PIP_INDEXES; do
      # All packages, more than 54000!
      new_zsh_all_pkgs+=( $(curl -s --max-time 30 $index \
        | sed -n '/<a href/ s/.*>\([^<]\{1,\}\).*/\1/p' \
        | tr '\n' ' ') )
    done

    if [[ $new_zsh_all_pkgs ]]; then
      __zsh_pip_all_pkgs=($new_zsh_all_pkgs)
      _store_cache pip_allpkgs __zsh_pip_all_pkgs
    else
      _message "Could not update package cache."
    fi
  fi
}

# Get installed packages, using pips completion interface.
_pip_installed() {
  installed_pkgs=($(_call_program fetch-installed \
    "env COMP_WORDS='pip uninstall' COMP_CWORD=2 PIP_AUTO_COMPLETE=1 $pip"))

  # TODO: using a cache might be benefical, but needs to cache by the "pip"
  # being used, which seems not to be worth it.
  # _pip_set_cache_policy
  #
  # if ( ! (( $+__zsh_pip_installed_pkgs )) || _cache_invalid pip_installedpkgs ) &&
  #   ! _retrieve_cache pip_installedpkgs;
  # then
  #   typeset -a -g __zsh_pip_installed_pkgs
  #   # __zsh_pip_installed_pkgs=($($pip freeze | cut -d '=' -f 1))
  #    __zsh_pip_installed_pkgs=($(_call_program fetch-installed \
  #      "env COMP_WORDS='pip uninstall' COMP_CWORD=2 PIP_AUTO_COMPLETE=1 $pip"))
  #   _store_cache pip_installedpkgs __zsh_pip_installed_pkgs
  # fi
}

_pip_set_cache_policy() {
  local cache_policy
  zstyle -s ":completion:${curcontext}:" cache-policy cache_policy
  if [[ -z "$cache_policy" ]]; then
    zstyle ":completion:${curcontext}:" cache-policy _pip_caching_policy
  fi
}

_pip_caching_policy() {
  if [[ ${1:t} == pip_allpkgs ]]; then
    # rebuild if cache is more than two weeks old
    local -a oldp
    oldp=( "$1"(Nm+14) )
    (( $#oldp ))

  else  # pip_installedpkgs
    # Compare cache file's timestamp to the most recently modified sys.path entry.
    # This gets changed/touched when installing removing packages.
    local newest_sys_path=$($python -c '
import sys
from os.path import exists, getmtime
print(sorted(sys.path, key=lambda x: exists(x) and getmtime(x))[-1])')
    [[ $newest_sys_path -nt $1 ]]
  fi
}


local -a common_ops
common_ops=(
  '(* : -)'{-h,--help}"[show help]"
  \*{-v,--verbose}"[give more output]"
  {-V,--version}"[show version and exit]"
  {-q,--quiet}"[give less output]"
  "--log=[log file where a complete record will be kept]:file"
  "--proxy=[specify a proxy in the form user:passwd@proxy.server:port]:proxy"
  "--timeout=[set the socket timeout (default 15 seconds)]:second"
  "--exists-action=[default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup]:action"
  "--cert=[path to alternate CA bundle]:path"
)

_requirements_file () {
  # Prefer requirement* and *.txt pattern. This falls back to "all files",
  # according to the file-patterns style.
  _wanted files expl file _files -g 'requirement*(-.)' -g '*.txt(-.)' "$@" -
}

typeset -A opt_args
local curcontext="$curcontext" state line ret=1
curcontext="${curcontext%:*}-$words[2]:"

_arguments -C \
  ':subcommand:->subcommand' \
  $common_ops \
  '*::options:->options' && ret=0

case $state in
  subcommand)
    local -a subcommands
    subcommands=(
      "install:install packages"
      "uninstall:uninstall packages"
      "freeze:output installed packages in requirements format"
      "list:list installed packages"
      "show:show information about installed packages"
      "search:search PyPI for packages"
      "wheel:build wheels from your requirements"
      "help:show available commands"

      "zip:zip dividual packages"
      "unzip:unzip undividual packages"
      "bundle:create pybundle"
    )

    _describe -t subcommands 'pip subcommand' subcommands && ret=0
  ;;

  options)
    local -a args
    args=(
      $common_ops
    )

    local -a pi_ops
    pi_ops=(
      {-i,--index-url=}"[base URL of Python Package Index]:URL"
      "--extra-index-url=[extra URLs of package indexes to use in addition to --index-url]:URL"
      "--no-index[ignore package index (only looking at --find-links URLs instead)]"
      {-f,--find-links=}"[URL to look for packages at]:URL"
      {-M,--use-mirrors}"[use the PyPI mirrors as a fallback in case the main index is down]"
      "--mirrors=[specific mirror URLs to query when --use-mirrors is used]:URL"
      "--allow-external=[allow the installation of externally hosted files]:package"
      "--allow-all-external[allow the installation of all externally hosted files]"
      "--no-allow-external[disallow the installation of all externally hosted files]"
      "--allow-insecure=[allow the installation of insecure and unverifiable files]:package"
      "--no-allow-insecure[disallow the installation of insecure and unverifiable files]"
    )

    case $words[1] in
      install | bundle)
        args+=(
          {-e,--editable=}"[install a package directly from a checkout]:directory or VCS+REPOS_URL[@REV]#egg=PACKAGE:_files -/"
          {-r,--requirement=}"[install all the packages listed in the given requirements file]:requirements file:_requirements_file"
          {-b,--build=}"[unpack packages into DIR]:directory:_directories"
          {-t,--target=}"[install packages into DIR]:directory:_directories"
          {-d,--download=}"[download packages into DIR instead of installing them]:directory:_directories"
          "--download-cache=[cache downloaded packages in DIR]:directory:_directories"
          "--src=[check out --editable packages into DIR]:directory:_directories"
          {-U,--upgrade}"[upgrade all packages to the newest available version]"
          "--force-reinstall[when upgrading, reinstall all packages even if they are already up-to-date]"
          {-I,--ignore-installed}"[ignore the installed packages]"
          "--no-deps[don't install package dependencies]"
          "--no-install[download and unpack all packages, but don't actually install them]"
          "--no-download[don't download any packages, just install the ones already downloaded]"
          "--install-option=[extra arguments to be supplied to the setup.py install command]:options"
          "--global-option=[extra global options to be supplied to the setup.py call before the install command]:options"
          "--user[install using the user scheme]"
          "--egg[install as self contained egg file, like easy_install does]"
          "--root=[install everything relative to this alternate root directory]:directory:_directories"
          "--use-wheel[find and prefer wheel archives when searching indexes and find-links locations]"
          "--pre[include pre-release and development versions]"
          "--no-clean[don't clean up build directories]"
          ':package name:->pkgs_all_and_dirs'

          $pi_ops
        )
      ;;

      uninstall)
        args+=(
          {-r,--requirement=}"[install all the packages listed in the given requirements file]::requirements file:_requirements_file"
          {-y,--yes}"[don't ask for confirmation of uninstall deletions]"
          ':installed package:->pkgs_installed'
        )
      ;;

      freeze)
        args+=(
          {-r,--requirement=}"[install all the packages listed in the given requirements file]::requirements file:_requirements_file"
          {-f,--find-links=}"[URL to look for packages at]:URL"
          {-l,--local}"[If in a virtualenv that has global access, do not list globally-installed packages]"
        )
      ;;

      list)
        args+=(
          {-o,--outdated}"[list outdated packages (excluding editables)]"
          {-u,--uptodated}"[list uptodated packages (excluding editables)]"
          {-e,--editable}"[list editable projects]"
          {-l,--local}"[If in a virtualenv that has global access, do not list globally-installed packages]"
          "--pre[include pre-release and development versions]"
          $pi_ops
        )
      ;;

      show)
        args+=(
          {-f,--files}"[show the full list of installed files for each package]"
          ':installed package:->pkgs_installed'
        )
      ;;

      search)
        args+=(
          "--index[base URL of Python Package Index]:URL"
        )
      ;;

      wheel)
        args+=(
          {-w,--wheel-dir=}"[build wheels into DIR, where the default is '<cwd>/wheelhouse']:directory:_directories"
          "--use-wheel[find and prefer wheel archives when searching indexes and find-links locations]"
          "--build-option=[extra arguments to be supplied to 'setup.py bdist_wheel']:options"
          {-r,--requirement=}"[install all the packages listed in the given requirements file]::requirements file:_requirements_file"
          "--download-cache=[cache downloaded packages in DIR]:directory:_directories"
          "--no-deps[don't install package dependencies]"
          {-b,--build=}"[directory to unpack packages into and build in]:directory:_directories"
          "--global-option=[extra global options to be supplied to the setup.py call before the 'bdist_wheel' command]:options"
          "--pre[include pre-release and development versions]"
          "--no-clean[don't clean up build directories]"
          $pi_ops
        )
      ;;

      unzip | zip)
        args+=(
          "--unzip[unzip a package]"
          "--no-pyc[do not include .pyc files in zip files]"
          {-l,--list}"[list the packages available, and their zip status]"
          "--sort-files[with --list, sort packages according to how many files they contain]"
          "--path=[restrict operation to the given paths]:paths"
          {-n,--simulate}"[do not actually perform the zip/unzip operation]"
        )
      ;;
    esac

    _arguments $args && ret=0

    # Additional states for expensive actions.
    case $state in
      pkgs_all_and_dirs)
          _pip_all
          _wanted all-packages expl 'packages' compadd -a __zsh_pip_all_pkgs && ret=0
          # TODO: only let _files fallback to dirs?  Use **/setup.py with _path_files and some limiting?
          _wanted directories expl 'directory with setup.py' _files -g '*/setup.py(:h/)' -s /setup.py && ret=0
        ;;

      pkgs_installed)
        local -a installed_pkgs
        _pip_installed
        _wanted installed-package expl 'installed packages' compadd -a installed_pkgs && ret=0
        ;;
    esac
  ;;
esac

return ret

diff --git a/_pip.zsh b/_pip
index c001bed..3e44cf2 100644
--- a/_pip.zsh
+++ b/_pip
@@ -146,6 +146,12 @@ _requirements_file () {
   _wanted files expl file _files -g 'requirement*(-.)' -g '*.txt(-.)' "$@" -
 }

+_constraints_file () {
+  # Prefer constraint* and *.txt pattern. This falls back to "all files",
+  # according to the file-patterns style.
+  _wanted files expl file _files -g 'constraint*(-.)' -g '*.txt(-.)' "$@" -
+}
+
 typeset -A opt_args
 local curcontext="$curcontext" state line ret=1
 curcontext="${curcontext%:*}-$words[2]:"
@@ -202,6 +208,7 @@ case $state in
         args+=(
           {-e,--editable=}"[install a package directly from a checkout]:directory or VCS+REPOS_URL[@REV]#egg=PACKAGE:_files -/"
           {-r,--requirement=}"[install all the packages listed in the given requirements file]:requirements file:_requirements_file"
+          {-c,--constraint=}"[constrain versions using the given constraints file]:constraints file:_constraints_file"
           {-b,--build=}"[unpack packages into DIR]:directory:_directories"
           {-t,--target=}"[install packages into DIR]:directory:_directories"
           {-d,--download=}"[download packages into DIR instead of installing them]:directory:_directories"
@@ -273,6 +280,7 @@ case $state in
           "--use-wheel[find and prefer wheel archives when searching indexes and find-links locations]"
           "--build-option=[extra arguments to be supplied to 'setup.py bdist_wheel']:options"
           {-r,--requirement=}"[install all the packages listed in the given requirements file]::requirements file:_requirements_file"
+          {-c,--constraint=}"[constrain versions using the given constraints file]:constraints file:_constraints_file"
           "--download-cache=[cache downloaded packages in DIR]:directory:_directories"
           "--no-deps[don't install package dependencies]"
           {-b,--build=}"[directory to unpack packages into and build in]:directory:_directories"

How to install it?