merge two dictionaries in a single expression
z = {**x, **y} #python 3.5 and above
z = x | y #python 3.9+ ONLY
def merge_two_dicts(x, y): # python 3.4 or lower
z = x.copy() # start with x's keys and values
z.update(y) # modifies z with y's keys and values & returns None
return z