def gprogrestion(lst):
    from math import sqrt
    if lst == []:
        return []
    else:
        if abs(lst[n]) == sqrt(lst[n-1]*lst[n+1]):
            return True
        else:
            return False

def gprogrestion(lst):
    from math import sqrt
    if lst == []:
        return ('Empty list')
    else:
        for x in lst:
            if abs(lst[x]) == sqrt(lst[x-1]*lst[x+1]):
                return True
            else:
                return False

def check_prog(lst):
    if len(lst) >= 3 and lst[1] != 0:
        for i in xrange(1, len(lst)-1):
            if not pow(lst[i-1] * lst[i+1], 0.5) == abs(lst[i]):
                return False
        return True
                
    elif len(lst) == 2 and all(lst):
        return True
        
if check_prog([1, 2, 4, 8]):
    print('this is a geometric progression')
else:
    print('this is not a geometric progression')

#!/usr/bin/env python3
 
def isgeompro(lst):
    """Test whether the list is a geometric progression."""
    if not (len(lst) >= 2 and lst[0] and lst[1]):
        return False
    q = lst[1] / lst[0]
    p = lst[1]
    for e in lst[2:]:
        # в p - элемент геом. прогрессии с коэфф. q
        if e / p == q:
            p = e
        else:
            return False
    return True

#!/usr/bin/env python3
 
from itertools import islice
 
def isgeompro(lst):
    """Test whether the list is a geometric progression."""
    if not (len(lst) >= 2 and lst[0] and lst[1]):
        return False
    q = lst[1] / lst[0]
    p = lst[1]
    for e in islice(lst, 2, None):
        # в p - элемент геом. прогрессии с коэфф. q
        if e / p == q:
            p = e
        else:
            return False
    return True

[1, 2, 3]

[guest@localhost timecmp]$ ./timecmp.py 
[1.0042134939999414, 1.025258840999868, 1.007287111000096]
[0.9715859099999307, 0.9866435950000323, 0.9697419239998908]
[0.9852825709999706, 0.988240076000011, 1.010458663999998]
[guest@localhost timecmp]$

lst[2:]

islice(lst, 2, None)

lst = [2, 4]
if len(lst) < 2:
    raise ValueError("len < 2")
l = lst[-1::-1]
s = map(lambda x: float(x[0])/x[1], zip(*[iter(l)]*2))
if len(lst) % 2:
    s.append(lst[0])
print len(set(s)) == 1