在实际写程序中，经常要对变量类型进行判断，除了用type(变量)这种方法外，还可以用isinstance方法判断：
a = 1
b = [1,2,3,4]
c = (1,2,3,4)
d = {'a':1, 'b':2, 'c':3}
e = "abc"
if isinstance(a,int):
print ("a is int")
else:
print ("a is not int")
if isinstance(b,list):
print ("b is list")
else:
print ("b is not list")
if isinstance(c,tupl
