Calculate the Hurwitz-Radon number of a positive integer

hurwitz_radon.py

def hurwitz_radon(n):
    '''Takes a positve integer n; returns the Hurwitz-Radon number p(n).
    p(n) defined as follows:
    Let n = (2^v)m with m odd and write v = 4a + b, 0<= b < 4.
    Then p(n) = 8a + 2^b.'''
    if not isinstance(n, int):
        raise TypeError("hurwitz_radon only defined for positive integers")
    if n <= 0:
        raise ValueError("hurwitz_radon only defined for positive integers")
    # helper to get largest power of 2 divinding n
    pow2 = lambda x : 0 if x%2 != 0 else (1 + pow2(x/2))
    v = pow2(n)
    a,b = divmod(v,4)
    return 8*a + 2**b


'''
## TESTS
if hurwitz_radon(8) == 8:
    print "Test #1 passed"
else:
    print "Test #1 failed"

if hurwitz_radon(9920) == 12:
    print "Test #2 passed"
else:
    print "Test #2 failed"

if hurwitz_radon(1671) == 1:
    print "Test #3 passed"
else:
    print "Test #3 failed"

try:
    hurwitz_radon(-5)
except ValueError:
    print "Test #4 passed"
except Exception:
    print "Test #4 failed"
else:
    print "Test #4 failed"

try:
    hurwitz_radon(1.0)
except TypeError:
    print "Test #5 passed"
except Exception:
    print "Test #5 failed"
else:
    print "Test #5 failed"

try:
    hurwitz_radon("Blistering barnacles")
except TypeError:
    print "Test #6 passed"
except Exception:
    print "Test #6 failed"
else:
    print "Test #6 failed"
'''