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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_value_contains(self, locator, expected, timeout=None):
 		"""Waits until the element identified by `locator` contains 		the expected value. You might want to use `Element Value Should Contain` instead. 		| *Argument* | *Description* | *Example* | 		| locator | Selenium 2 element locator | id=my_id | 		| expected | expected value | Slim Shady | 		| timeout | maximum time to wait before the function throws an element not found error (default=None) | 5s |"""


		self._info("Waiting for '%s' value to contain '%s'" % (locator, expected))
		self._wait_until_no_error(timeout, self._check_element_value_exp, True, locator, expected, False, timeout)