'''20210921

Robin Dawes
'''


def dot_product(vec1, vec2):
   '''
   Compute the dot product of two numeric vectors represented as lists
   
   Parameters:  vec1 and vec2 must be numeric vectors of equal length
   
   Returns a numeric value if the dot product can be computed.
   Returns None if the dot product cannot be computed.
   '''
   
   if not(type(vec1) is list)  or not(type(vec2) is list):
      return None
   elif len(vec1) != len(vec2):
      return None
   else:
      result = 0
      for i in range(len(vec1)):
         if isinstance(vec1[i], (int, float)) and isinstance(vec2[i],(int, float)):
            result += vec1[i] * vec2[i]
         else:
            return None
      return result
      
      
def test_dot_product_1():
   '''This test should fail - it is included to demonstrate what pytest
      does when a test fails'''
   assert dot_product([2],[3]) == 0
   
def test_dot_product_2():
   assert dot_product([1,1],[2,3]) == 5
   
def test_dot_product_3():
   assert dot_product('a',[2,3,4]) == None

def test_dot_product_4():
   assert dot_product([1,2],[1,2,3]) == None
   
def test_dot_product_5():
   assert dot_product([1,1],['a','b']) == None