assertExist and assert Env.getClipboard() not wroking

how does assertExist ("img.png") work .. during run process is shows not assertExist not define.
same problem occurs with assert Env.getClipboard()

def setUp(self):
    setAutoWaitTimeout(10)
    openApp("C:\\Windows\\system32\calc.exe") # open windows calculator
    wait("CalculatorWindow.png") # wait for calculator window to appear

def test_calculator(self):
    with Region(find("CalculatorWindow.png")):
        click("1_Button.png") # Click "1"
        click("Plus_Button.png") # Click "+"
        click("2_Button.png") # Click "2"
        click("Equals_Button.png") # Click "="
    type("c",KEY_CTRL)
    assert Env.getClipboard() == 3 # not working (assert Env.getClipboard())

def tearDown(self):
    closeApp("Calculator") # Matches text from the window's title bar