def find_min_and_max(L):
if not L:
# return (None, None)
return None, None
elif len(L) == 1:
return L[0], L[0]
max, min = None, None
for i in L:
if max is None and min is None:
# 0不是None
# None不推荐使用=
# Python可以 max==min==None
max = i
min = i
continue;
if i > max:
max = i
elif i < min:
min = i
return min, max
煎饼果子