Enables one to merge dictionaries in Python whilst preserving previous keys.

dictmerge.py

def dictmerge(target, *args):
    '''
    Merge multiple dictionaries.
    Usage:
    
        one = {'one': 1}
        two = {'two': 2}
        three = {'three': 3}
        sum = dictmerge(one, two, three)
        
        {one: 1, two: 2, three: 3}
    '''
    target = copy.deepcopy(target)
    if len(args) > 1:
        for obj in args:
            target = dictmerge(target, obj)
        return target
    obj = copy.deepcopy(args[0])

    # Try to combine basic algorithms we know will work for sure.
    try:
        if isinstance(target, (bool, int, float, str, list, tuple, set)) and isinstance(obj, (bool, int, float, str, list, tuple, set)):
            if isinstance(target, bool) and isinstance(obj, bool):
                return target and obj
            if isinstance(target, (int, float)) and isinstance(obj, (int, float)):
                return target + obj
            if isinstance(target, (list, tuple, set)) and isinstance(obj, (list, tuple, set)):
                return list(target + obj)
            raise ValueError('Invalid Argument')
        elif isinstance(target, dict) and isinstance(obj, dict):
            # Don't take action on dictionaries. We will execute on them in the following lines after the exception tracking.
            pass
        else:
            raise ValueError('Invalid Argument')
    except Exception as e:
        raise ValueError('\x1b[33mCould not merge\x1b[0m %s(%s) and %s(%s); Error=%s' % (type(target), target, type(obj), obj, e) )

    # Recursively merge dicts and set non-dict values
    for k, v in list(obj.items()):
        if k in target and isinstance(v, dict):
            target[k] = dictmerge(target[k], v)
        elif k in target and isinstance(v, (set, tuple, list)):
            target[k] = target[k] + v
        else:
            target[k] = v
    return target