move imports to top of files
add from __future__ import
commands module -> subprocesses module
print statement -> print() function
exec statement -> exec() function
xrange -> range
map() -> list(map())
StandardError -> Exception
integer division: / -> //
x.has_key(y) -> y in x
sort(): use functools.cmp_to_key
type(x) is y -> isinstance(x, y)
raw_input -> input
change variable names 'list' to avoid clashes with list class
