{"id":28782,"date":"2023-01-02T20:31:03","date_gmt":"2023-01-02T15:01:03","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-for-loop-returning-unexpected-values-when-squaring-values\/"},"modified":"2023-01-02T20:31:03","modified_gmt":"2023-01-02T15:01:03","slug":"solved-for-loop-returning-unexpected-values-when-squaring-values","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-for-loop-returning-unexpected-values-when-squaring-values\/","title":{"rendered":"[Solved] for loop returning unexpected values when squaring values"},"content":{"rendered":"

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You iterate over the list by using for elem in testList<\/code>, which yields elements of the list and not their indices.<\/p>\n

>>> b = [1, 3, -4, 5, 5, 3, 2, 1, 4, 8, 9]\n>>> for i in b:\n        print i,\n\n\n1 3 -4 5 5 3 2 1 4 8 9 # Whereas you expected 0 1 2 3 4 5 6 7 8 9 10\n<\/code><\/pre>\n
So, your code fetches the elements using the values as the indices and returns the square of those values. This is what happens –<\/p>\n
>>> for index, val in enumerate(b): # enumerate yields an (index, value) tuple which gets unpacked.\n        print '{0} : {1}*{1} = {2}'.format(index, val, val**2)\n\n\n0 : 1*1 = 1\n1 : 3*3 = 9\n2 : -4*-4 = 16\n3 : 5*5 = 25\n4 : 5*5 = 25\n5 : 3*3 = 9\n6 : 2*2 = 4\n7 : 1*1 = 1\n8 : 4*4 = 16\n9 : 8*8 = 64\n10 : 9*9 = 81\n<\/code><\/pre>\n
Whereas in your initial code, the a<\/code> list happens to be the indices you’re expecting<\/strong> which builds up the correct list as you observed.<\/p>\n
Easier Solutions<\/strong> – <\/p>\n
You could use a list comprehension to build up your lists, like (No Need to multiply a number by itself if you’re looking for it’s square, just use the builtin exponentiation operator (**<\/code>))<\/p>\n
>>> [elem**2 for elem in a]\n[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]\n>>> [elem**2 for elem in b]\n[1, 9, 16, 25, 25, 9, 4, 1, 16, 64, 81]\n<\/code><\/pre>\n
Or a solution using map<\/code>.<\/p>\n
>>> map(lambda x: x**2, a)\n[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]\n>>> map(lambda x: x**2, b)\n[1, 9, 16, 25, 25, 9, 4, 1, 16, 64, 81]\n<\/code><\/pre>\n<\/p><\/div>\n
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solved for loop returning unexpected values when squaring values <\/p>\n","protected":false},"excerpt":{"rendered":"
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