title: unsupported format character '%' error as I try to create logs
body: <p>I am trying to create a simple log file using the following code.</p>
  
  <pre><code>import logging
  
  format = '%(asctime) %(message)'
  
  logging.basicConfig(format=format)
  log_message = {'service': 'test-service', 'm': 'service started successfuly!'}
  logger = logging.getLogger('root-logger')
  
  logger.warning('this is a test log message %s', extra = log_message)
  </code></pre>
  
  <p>But as I try to execute the above code, I get an error saying:</p>
  
  <pre><code>    --- Logging error ---
  Traceback (most recent call last):
  File "/Users/pc/anaconda3/envs/spider/lib/python3.7/logging/__init__.py", line 1025, in emit
      msg = self.format(record)
  File "/Users/pc/anaconda3/envs/spider/lib/python3.7/logging/__init__.py", line 869, in format
      return fmt.format(record)
  File "/Users/pc/anaconda3/envs/spider/lib/python3.7/logging/__init__.py", line 611, in format
      s = self.formatMessage(record)
  File "/Users/pc/anaconda3/envs/spider/lib/python3.7/logging/__init__.py", line 580, in formatMessage
      return self._style.format(record)
  File "/Users/pc/anaconda3/envs/spider/lib/python3.7/logging/__init__.py", line 422, in format
      return self._fmt % record.__dict__
  ValueError: unsupported format character '%' (0x25) at index 11
  Call stack:
  File "test.py", line 9, in &lt;module&gt;
      logger.warning('this is a test log message %s', extra = log_message)
  Message: 'this is a test log message %s'
  Arguments: ()
  </code></pre>
  
  <p>I cannot understand the error.What could be the reason for this error?</p>