code: def install_dependencies(feature=None):
      
      import subprocess
  
      echo(green('\nInstall dependencies:'))
      echo(green('-' * 40))
  
      req_path = os.path.realpath(os.path.dirname(__file__) + '/../_requirements')
  
      # list all features if no feature name
      if not feature:
          echo(yellow('Please specify a feature to install. \n'))
          for index, item in enumerate(os.listdir(req_path)):
              item = item.replace('.txt', '')
              echo(green('{}. {}'.format(index + 1, item)))
  
          echo()
          return
  
      # install if got feature name
      feature_file = feature.lower() + '.txt'
      feature_reqs = os.path.join(req_path, feature_file)
  
      # check existence
      if not os.path.isfile(feature_reqs):
          msg = 'Unable to locate feature requirements file [{}]'
          echo(red(msg.format(feature_file)) + '\n')
          return
  
      msg = 'Now installing dependencies for "{}" feature...'.format(feature)
      echo(yellow(msg))
  
      subprocess.check_call([
          sys.executable, '-m', 'pip', 'install', '-r', feature_reqs]
      )
  
      # update requirements file with dependencies
      reqs = os.path.join(os.getcwd(), 'requirements.txt')
      if os.path.exists(reqs):
          with open(reqs) as file:
              existing = [x.strip().split('==')[0] for x in file.readlines() if x]
  
          lines = ['\n']
          with open(feature_reqs) as file:
              incoming = file.readlines()
  
              for line in incoming:
                  if not(len(line)) or line.startswith('#'):
                      lines.append(line)
                      continue
  
                  package = line.strip().split('==')[0]
                  if package not in existing:
                      lines.append(line)
  
          with open(reqs, 'a') as file:
              file.writelines(lines)
  
      echo(green('DONE\n'))
docs: Install dependencies for a feature