check variables, stop program and give useful error message
# check if mylist is really a list
mylist=4
if not isinstance(mylist,list):
raise TypeError('mylist is not a list')
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
TypeError: Mylist is not a list
# check if 'data' is numberic
data=['A','B']
if not isinstance(data,(int,float)):
raise TypeError('data is not a number')
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
TypeError: data is not a number
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