title: How to add a screenshot to allure report with python?
body: <p>I have this code:</p>
  
  <pre><code># coding: utf-8
  from selenium import webdriver
  import pytest
  import allure
  
  
  @pytest.yield_fixture(scope='session')
  def driver():
      _driver = webdriver.PhantomJS()
      yield _driver
      _driver.quit()
  
  
  def test_ya(driver):
      with allure.step('open ya.ru and take screenshot'):
          driver.get('http://ya.ru/')            
          allure.attach('screenshot', driver.get_screenshot_as_png(), type='png')
  </code></pre>
  
  <p>and I try to take a screenshot and save it to allure report,
  after execution I have:</p>
  
  <pre><code>&gt;       with self._attachfile("%s-attachment.%s" % (uuid.uuid4(), attach_type.extension)) as f:
              if isinstance(body, text_type):
  E           AttributeError: 'str' object has no attribute 'extension'
  </code></pre>
  
  <p>How can I fix this?</p>