A quick Ruby wrapper for manipulating Python's virtual environments.

pyvirtualenv.rb

require 'open3'

class VirtualEnvError < Exception; end

class PythonVirtualEnv

  def self.exists?(path)
    File.directory?(path) and File.exists?(File.join(path, 'bin/activate'))
  end

  def initialize(path)
    @env_path = path
    @activate_path = File.join(@env_path, 'bin/activate')
    self.create! unless self.exists?
  end

  def exists?
    File.directory?(@env_path) and File.exists?(@activate_path)
  end

  def create!
    status_code, _, _ = self.cmd("virtualenv #{@env_path}")
    if status_code != 0
      raise VirtualEnvError, "Failed to create virtualenv: #{output}"
    end
  end

  def cmd(cmd)
    # HACK: fix leaking env vars to the pip subprocess's git subprocess
    env = {'GIT_DIR'=>nil, 'GIT_WORK_TREE'=>nil, 'GIT_INDEX_FILE'=>nil}
    
    # run the command
    Open3.popen3(env, cmd) do |stdin, stdout, stderr, wait_thr|
      # read the stream contents
      output = stdout.read
      errors = stderr.read
      # wait for the process to exit
      pid = wait_thr.pid # pid of the started process.
      exit_status = wait_thr.value # Process::Status object returned.
      # close each stream
      stdin.close
      stdout.close
      stderr.close
      # return the response
      return exit_status, output, errors
    end
  end

  def exec(cmd)
    status, output, err = self.cmd("source #{@activate_path} && #{cmd}")
    return status, output, err
  end

  def install_dependencies(path)
    pip_path = File.join(@env_path, 'bin', 'pip')
    exit_code, output, err = self.cmd("#{pip_path} install -r #{path}")
    if exit_code != 0
      raise VirtualEnvError, "Failed to install pip dependencies: #{exit_code} #{output} #{err}"
    end
    return exit_code, output, err
  end

  def path
    return @env_path
  end

  def binary(name)
    bin_path = File.join(@env_path, 'bin', name)
    unless File.exists?(bin_path)
      raise VirtualEnvError, "No such binary in environment: #{name}"
    end
    return bin_path
  end

  def packages
    pip_path = File.join(@env_path, 'bin', 'pip')
    exit_code, output, err = self.cmd("#{pip_path} list")
    if exit_code != 0
      raise VirtualEnvError, "Could not list packages: #{err}"
    end
    # extract matches (ugly hack)
    matches = output.to_enum(:scan, /([a-zA-Z0-9\.\-]+)\s+\(([a-zA-Z0-9\.\-]+)/).map { Regexp.last_match }
    # build a hash of package names to versions
    packages = {}
    matches.each do |match|
      packages[match[1]] = match[2]
    end
    return packages
  end

end

### USAGE ###
env = PythonVirtualEnv.new('/path/to/virtualenv') # will be created if non-existent
env.install_dependencies('requirements.txt')
env.packages # => {"requests" => "2.1.0", ...}
env.exec("binary_name arg0 arg1 ...") # => [return_code, stdout, stderr]