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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def wait_until_element_has_focus(self, locator, timeout=None):
 		"""Waits until the element identified by `locator` has focus. 		You might rather want to use `Element Focus Should Be Set` 		| *Argument* | *Description* | *Example* | 		| locator | Selenium 2 element locator | id=my_id | 		| timeout | maximum time to wait before the function throws an element not found error (default=None) | 5s |"""


		self._info("Waiting for focus on '%s'" % (locator))
		self._wait_until_no_error(timeout, self._check_element_focus_exp, True, locator, timeout)