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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 set_element_focus(self, locator):
 		"""Sets focus on the element identified by `locator`. Should 		be used with elements meant to have focus only, such as 		text fields. This keywords also waits for the focus to be 		active by calling the `Wait Until Element Has Focus` keyword. 		| *Argument* | *Description* | *Example* | 		| locator | Selenium 2 element locator | id=my_id |"""


		self._info("Setting focus on element '%s'" % (locator))
		
		element = self._element_find(locator, True, True)
		element.send_keys(Keys.NULL)

		self._wait_until_no_error(None, self._check_element_focus, True, locator)