[Python] Text widget updates only after calling method exits (threading issue?)

Are Tkinter widgets running on their own thread?

If I try to make a simple application that will print the letters A to
Z to a Tkinter Text widget, and I space the printing of each letter by
1 second, it seems no text will appear in the Text widget until the
method exits.

Take a look at this snippet:

# Assume I have created no threads other than the one that comes
with Main

def printToTkinterTextWidget(text):
"""
Prints A-Z to the Text widget, 1 letter per second.
"""
# Problem: no text appears in the widget until 26 seconds has
elapsed
for aNumber in range(65, 91):
self.textWidget.insert(END, text)
time.sleep(1)

If I am supposed to send messages to Tkinter objects only from the
main thread, how can I get the letters to appear 1 per second?

Thanks,

Mario