Make code more pythonic (4)

- sort imports
- use python commands whenever possible (os.remove...)
- keep one argument per line on methods with long arguments
- no need to put parenthesis around simple conditionals
- if a variable defined in the global scope is not going to be
  modified, there's no need to use the global statement (the other
  way around is also true, if it will be updated the global
  statement is mandatory)
- use single quotes whenever possible
- use the new string formatting syntax