true, and i can't think of a legitimate case where it would have tripped me up. but if someone, a novice perhaps, wrote

def some_func(foo, bar=[1, 2, 3]):
    bar.reverse()  # for whatever reason
    print(bar)

some_func('hello')    # output [3,2,1]
some_func('hello')    # output [1,2,3] 

i think they would be within their rights to be surprised that calling this function twice has different results. that's what i was surprised by; it feels like bar would be re initialised each time with a scope of the function but apparenty not