On Wednesday 09 March 2016 16:27, Veek. M wrote:
> What is the return value of `exec`? Would that object be then used to
> iterate the sequence in 'a'? I'm reading this:
> https://www.python.org/download/releases/2.2.3/descrintro/
exec is a statement, not a function, so it doesn't have a return value.
Are you referring to this line of code?
exec "x = 3; print x" in a
That doesn't return a value. The "in a" part tells exec which namespace to
execute the code in. It doesn't mean "test if the result is found inside
sequence a".
py> namespace = {'__builtins__': None}
py> exec "x = 3" in namespace
py> namespace
{'__builtins__': None, 'x': 3}
If you leave the "in namespace" part out, then exec will use the current
namespace, and x will become a local variable.
What happens if you don't put the special __builtins__ key into the
namespace? Python adds it for you:
py> mydict = {}
py> exec "foo = 99.99" in mydict
py> mydict.keys()
['__builtins__', 'foo']
What's inside __builtins__? Every single built-in function and class:
py> mydict['__builtins__']
{'bytearray': <type 'bytearray'>, 'IndexError': <type
'exceptions.IndexError'>, 'all': <built-in function all>,
... dozens more entries ...
'OverflowError': <type 'exceptions.OverflowError'>}
--
Steve
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