Benchmarks !

With: IPython and it's magic function %timeit

#1 Count elements in list

# SLOW
how_many = 0
for element in BIG_LIST:
    how_many += 1
print how_many

# FAST
print len(BIG_LIST)

For 1 000 000 elements it's 26.5 ms vs 96.7 ns
274 000 times faster actually