python - Try-clause containing multiple statements -

let's have following function/method, calculates bunch of stuff , sets lot variables/attributes: calc_and_set(obj).

now call function several times different objects, , if 1 or more fails nothing should set @ all.

i thought this:

try:   calc_and_set(obj1)   calc_and_set(obj2)   calc_and_set(obj3) except:   pass 

but doesn't work. if instance error happens in third call function, first , second call have set variables.

can think of "clean" way of doing want? solutions can think of rather ugly workarounds.

i see few options here.

a. have "reverse function", robust. if

def calc_and_set(obj):     obj.a = 'a'  def unset(obj):     if hasattr(obj, 'a'):         del obj.a 

and

try:   calc_and_set(obj1)   calc_and_set(obj2) except:   unset(obj1)   unset(obj2) 

notice, in case, unset doesn't care if calc_and_set completed or not.

b. separate calc_and_set try_calc_and_set, testing if works, , set, won't throw errors, , called if try_calc_and_set didn't fail.

try:   try_calc_and_set(obj1)   try_calc_and_set(obj2)   calc_and_set(obj1)   calc_and_set(obj2) except:   pass 

c. (my favorite) - have calc_and_set return new variable, , not operate in place. if successful, replace original reference new one. done adding copy first statement in calc_and_set, , returning variable.

try:   obj1_t = calc_and_set(obj1)   obj2_t = calc_and_set(obj2)   obj1 = obj1_t   obj2 = obj2_t except:   pass 

the mirror of 1 of course save objects before:

obj1_c = deepcopy(obj1) obj2_c = deepcopy(obj2) try:   calc_and_set(obj1)   calc_and_set(obj2) except:   obj1 = obj1_c   obj2 = obj2_c 

and general comment (if sample code, forgive me) - don't have excepts without specifying exception type.