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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 element_value_should_contain(self, locator, expected):
 		"""Verifies the element identified by `locator` contains the expected value. 		| *Argument* | *Description* | *Example* | 		| locator | Selenium 2 element locator | id=my_id | 		| expected | expected value | Slim Shady |"""


		self._info("Verifying element '%s' value contains '%s'" % (locator, expected))
		
		element = self._element_find(locator, True, True)
		value = str(element.get_attribute('value'))
		
		if expected in value:
			return
		
		else:
			raise AssertionError("Value '%s' did not appear in element '%s'. It's value was '%s'" % (expected, locator, value))