Comparing Python objects from deepcopy

Question

Is there a way to compare a Python object with an object generated from a deepcopy?

eg:

    import copy 

    original_object = SomeObject()
    cloned_object = copy.deepcopy(original_object)
    assertDeepCopy(original_object, cloned_object)

Answer 1

This is what I believe you're asking for:

def deep_compare(left, right):
    try:
        if not left.__dict__:
            return left == right

        for key in left.__dict__:
            if key not in right.__dict__:
                return false
            else:
                return deep_compare(left[key], right[key])
    except (AttributeError, TypeError):
        return left == right 

However, note that this can go wrong in a number of places: if the objects don't define == in a way that you like, you won't get the answer that you want.

Answer 2

I know it is an old answer, but with Python 3 the previous code didn't work for me, so I updated it in this one that works better for me:

import logging
log = logging.getLogger(__name__)

...

    def deep_compare(self,left, right, level=0):
        if type(left) != type(right):
            log.info("Exit 1 - Different types")
            return False

        elif type(left) is dict:
            # Dict comparison
            for key in left:
                if key not in right:
                    log.info("Exit 2 - missing {} in right".format(key))
                    return False
                else:
                    if not deep_compare(left[str(key)], right[str(key)], level +1 ):
                        log.info("Exit 3 - different children")
                        return False
            return True
        elif type(left) is list:
            # List comparison
            for key in left:
                if key not in right:
                    log.info("Exit 4 - missing {} in right".format(key))
                    return False
                else:
                    if not deep_compare(left[left.index(key)], right[right.index(key)], level +1 ):
                        log.info("Exit 5 - different children")
                        return False
            return True
        else:
            # Other comparison
            return left == right

        return False

It compares dict, list and any other types that implements the "==" operator by themselves. If you need to compare something else different, you need to add a new branch in the "if tree".

Hope that helps.

Answer 3

This solution allows you to to deep compare objects, dicts, lists and primitives. And it allows you to exclude keys from the comparison.

I thought this might be helpful to some people looking for deep compare with object support :)

def deep_compare(left, right, excluded_keys = []):
    # convert left and right to dicts if possible, skip if they can't be converted
    try: 
        left = left.__dict__
        right = right.__dict__
    except:
        pass

    # both sides must be of the same type 
    if type(left) != type(right):
        return False

    # compare the two objects or dicts key by key
    if type(left) == dict:
        for key in left:
            # make sure that we did not exclude this key
            if key not in excluded_keys:
                # check if the key is present in the right dict, if not, we are not equals
                if key not in right:
                    return False
                else:
                    # compare the values if the key is present in both sides
                    if not deep_compare(left[key], right[key], excluded_keys):
                        return False

        # check if any keys are present in right, but not in left
        for key in right:
            if key not in left and key not in excluded_keys:
                return False
        
        return True

    # check for each item in lists
    if type(left) == list:
        # right and left must have the same length
        if len(left) != len(right):
            return False

        # compare each item in the list
        for index in range(len(left)):
            if not deep_compare(left[index], right[index], excluded_keys):
                return False

    # do a standard comparison
    return left == right