Is there a greater than but less than function in python?

In Python you can even write

while 10 < a < 20:
    do_smth()

while 10 < a < 20:
    whatever

This doesn't work in most languages, but Python supports it. Note that you should probably be using a for loop:

for a in range(11, 20):
    whatever

or if you just want to test a single number rather than looping, use an if:

if 10 < a < 20:
    whatever

Be careful with the boundary conditions. When your first loop ends, a is set to 10. (In fact, it's already set to 10 when you print the last "less than 10" message.) If you immediately check whether it's greater than 10, you'll find it's not.