ATOmac - waitForWindowToAppear returns False every time

Question

I am using Atomac (https://pypi.python.org/pypi/atomac/1.1.0) to automate a Mac application. I want to wait for a window to be appear(or disappear) and I saw in the documentations that are functions for this:(https://github.com/ldtp/pyatom/blob/master/atomac/AXClasses.py)

However, when I am testing waitForWindowToAppear function, it always returns False, for example:

import atomac
atomac.launchAppByBundleId("com.apple.Safari")
app = atomac.getAppRefByBundleId("com.apple.Safari")
window = app.waitForWindowToAppear("Safari", 10)
print window #False