For statements, use
exec(string) (Python 2/3) or
exec string (Python 2):
>>> mycode="print "hello world"" >>> exec(mycode) Hello world
When you need the value of an expression, use
>>> x = eval("2+2") >>> x 4
However, the first step should be to ask yourself if you really need to. Executing code should generally be the position of last resort: It’s slow, ugly and dangerous if it can contain user-entered code. You should always look at alternatives first, such as higher order functions, to see if these can better meet your needs.