Drawing inverted triangles
Decorators are a tool that you use when you have many functions that share a behaviour, for example a particular calling convention or treatment of results. See the Python Decorator Library on the Python wiki for some examples, and this answer on Stack Overflow for a tutorial.

Here you only have two functions, so it doesn't seem likely that decorators will be helpful. Use the right tool for the job!

Anyway, comments on your code.


No docstrings! What do these functions do and how do you call them?
The else: continue in get_rows() is unnecessary.
The regular keyword argument to triangle is ignored.
Your function triangle seems very long for what it's doing. Why not use Python's format language to do the padding? Like this:

def triangle(n, invert=True):
    """Print inverted triangle of asterisks (with `n`+1 rows) to standard output.
    Print it the right way up if keyword argument `invert=False` is given.
    """
    for i in reversed(xrange(n + 1)) if invert else xrange(n + 1):
        print('{:&gt;{}}{:&gt;{}}'.format('*', n - i + 1, '*' if i else '', 2 * i))