scripts/virtualenv_wrapper.py

#!/usr/bin/env python2
# Copyright 2016 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Wrapper around chromite executable scripts that use virtualenv."""

from __future__ import print_function

import os
import subprocess
import sys

import wrapper

_CHROMITE_DIR = os.path.realpath(
    os.path.join(os.path.abspath(__file__), '..', '..'))

# _VIRTUALENV_DIR contains the scripts for working with venvs
_VIRTUALENV_DIR = os.path.join(_CHROMITE_DIR, '..', 'infra_virtualenv')
_CREATE_VENV_PATH = os.path.join(_VIRTUALENV_DIR, 'bin', 'create_venv')
_REQUIREMENTS = os.path.join(_CHROMITE_DIR, 'venv', 'requirements.txt')

_VENV_MARKER = 'INSIDE_CHROMITE_VENV'


def main():
  if _IsInsideVenv(os.environ):
    wrapper.DoMain()
  else:
    venvdir = _CreateVenv()
    _ExecInVenv(venvdir, sys.argv)


def _CreateVenv():
  """Create or update chromite venv."""
  return subprocess.check_output([
      _CREATE_VENV_PATH,
      _REQUIREMENTS,
  ]).rstrip()


def _ExecInVenv(venvdir, args):
  """Exec command in chromite venv.

  Args:
    venvdir: virtualenv directory
    args: Sequence of arguments.
  """
  venv_python = os.path.join(venvdir, 'bin', 'python')
  os.execve(
      venv_python,
      [venv_python] + list(args),
      _CreateVenvEnvironment(os.environ))


def _CreateVenvEnvironment(env_dict):
  """Create environment for a virtualenv.

  This adds a special marker variable to a copy of the input environment dict
  and returns the copy.

  Args:
    env_dict: Environment variable dict to use as base, which is not modified.

  Returns:
    New environment dict for a virtualenv.
  """
  new_env_dict = env_dict.copy()
  new_env_dict[_VENV_MARKER] = '1'
  new_env_dict.pop('PYTHONPATH', None)
  return new_env_dict


def _IsInsideVenv(env_dict):
  """Return whether the environment dict is running inside a virtualenv.

  This checks the environment dict for the special marker added by
  _CreateVenvEnvironment().

  Args:
    env_dict: Environment variable dict to check

  Returns:
    A true value if inside virtualenv, else a false value.
  """
  # Checking sys.prefix or doing any kind of path check is unreliable because
  # we check out chromite to weird places.
  return env_dict.get(_VENV_MARKER, '')


if __name__ == '__main__':
  main()