Converting a flat list to a list of tuples

[metiu uitem]

Say you have a flat list:
['a', 1, 'b', 2, 'c', 3]

How do you efficiently get
[['a', 1], ['b', 2], ['c', 3]]

I was thinking of something along the lines of:
for (key,number) in list:
  print key, number

but it's not working...

Thank you