1.

def getsuff(s):
   tmp = s.split('.')
   if len(tmp) == 1: return None
   return tmp[-1]

print getsuff('abc.de.f')
print getsuff('abc de f')

2.

def nrowcol(m):
  nr = len(m)
  nc = len(m[0])
  return nr,nc

a = [[5,1],[12,8],[13,88]]
print nrowcol(a)  # prints (3,2)

3.

def bigsum(x):
   tot = 0  
   for i in x:
      if type(i) is list: tot +=  bigsum(i)
      else: tot += i
   return tot

a = [5,12,13]
b = [2,a]
c = [3,[8,a,b]]
d = [[8,a,b],b,1]
print bigsum(a)
print bigsum(b)
print bigsum(c)
print bigsum(d)