How to create independent objects

Question

I'm having a problem with two objects I created. I have a while loop getting some data. I save this data in an object and on each loop I want to see if my data has changed. If its true I save the data on a log. The problem is that when I refresh my actVar my prevVar is getting this changed too. This is my code:

I tried to use the copy() function with no success

uvcomsSup = UVCEComsCtrl_SupportData()
uvcomsAntSup = UVCEComsCtrl_SupportData()
while 1:
 try: 
 uvcomsSup = getUVComsSupport(OrigAddress, UVComsDestAddress) 
 print(uvcomsSup)
 print("________________________")
 print(uvcomsAntSup) 
 print(uvcomsSup is uvcomsAntSup)
 if (uvcomsSup != uvcomsAntSup):
 uvcomsAntSup = copy.copy(uvcomsSup) 
 logFile.addSupportData(str(uvcomsSup)) 
 sleep(1)
 except Exception as err:
 print("Error inesperado:", sys.exc_info()[0])
 print(err)

When I print this two objects (I have an eq method and str method) I see the same values. I just enter in the if condition the first time.

Any help?

Thank you

• dallonsi: Try to use deepcopy instead of copy

Answer 1

I cannot run your code so I cannot see the whole picture.

However I can see you are returning a shallow copy of ucomsSup, which retains references to the original object thus modifying it.

Try using a deep copy instead.

uvcomsSup = UVCEComsCtrl_SupportData()
uvcomsAntSup = UVCEComsCtrl_SupportData()
while 1:
 try: 
 uvcomsSup = getUVComsSupport(OrigAddress, UVComsDestAddress) 
 print(uvcomsSup)
 print("________________________")
 print(uvcomsAntSup) 
 print(uvcomsSup is uvcomsAntSup)
 if (uvcomsSup != uvcomsAntSup):
 uvcomsAntSup = copy.deepcopy(uvcomsSup) ## Create deep copy 
 logFile.addSupportData(str(uvcomsSup)) 
 sleep(1)
 except Exception as err:
 print("Error inesperado:", sys.exc_info()[0])
 print(err)

Answer 2

The Python docs say:

copy(x) Return a shallow copy of x.

A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.

Try using copy.deepcopy(x) instead.

uvcomsAntSup = copy.deepcopy(uvcomsSup) 

copy.deepcopy(x) Return a deep copy of x.

A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.

Read more about this: https://docs.python.org/3.7/library/copy.html