code: def acquire(self):
          '''
          Returns an available instance.
  
          Returns:
              browser from pool, if available
  
          Raises:
              NoBrowsersAvailable if none available
          '''
          with self._lock:
              if len(self._in_use) >= self.size:
                  raise NoBrowsersAvailable
              browser = self._fresh_browser()
              self._in_use.add(browser)
              return browsef acquire(self):
          '''
          Returns an available instance.
  
          Returns:
              browser from pool, if available
  
          Raises:
              NoBrowsersAvailable if none available
          '''
          with self._lock:
              if len(self._in_use) >= self.size:
                  raise NoBrowsersAvailable
              browser = self._fresh_browser()
              self._in_use.add(browser)
              return browser
docs: Returns an available instance.
  
          Returns:
              browser from pool, if available
  
          Raises:
              NoBrowsersAvailable if none available