exec "statement" VS. exec "statement in globals(), locals()

[Ted]

--------
def f():
ret = 2
exec "ret += 10"
return ret

print f()
--------

The above example prints '12'. However, the following example prints
'2':

--------
def f():
ret = 2
exec "ret += 10" in globals(), locals()
return ret

print f()
--------

According to (http://docs.python.org/ref/exec.html), "In all cases, if
the optional parts are omitted, the code is executed in the current
scope." Don't globals() and locals() comprise the current scope? Why
isn't the output of each example the same?

[Duncan Booth]

ro*******@gmail .com (Ted) wrote in
news:9a******** *************** ***@posting.goo gle.com:

According to (http://docs.python.org/ref/exec.html), "In all cases, if
the optional parts are omitted, the code is executed in the current
scope." Don't globals() and locals() comprise the current scope? Why
isn't the output of each example the same?

locals() is a copy of the current scope, not the original. You should never
expect updates to locals() to be reflected in the local variables of the
current scope.

Are you really sure you need to use exec at all? There are very few good
use cases where exec is the appropriate answer to a problem.