Unable to exceute mean of list of lists I have a list of lists of the following type  

a=[[0.        , 0.03846154, 0.34615385, 0.34615385, 0.42307692,
       0.42307692, 0.53846154, 0.53846154, 0.61538462, 0.61538462,
       0.65384615, 0.65384615, 0.73076923, 0.73076923, 0.76923077,
       0.76923077, 0.80769231, 0.80769231, 0.88461538, 0.88461538,
       0.92307692, 0.92307692, 0.96153846, 0.96153846, 1.        ,
       1.        ], [0.        , 0.03846154, 0.61538462, 0.61538462, 0.69230769,
       0.69230769, 0.73076923, 0.73076923, 0.76923077, 0.76923077,
       0.80769231, 0.80769231, 0.84615385, 0.84615385, 0.88461538,
       0.88461538, 0.92307692, 0.92307692, 0.96153846, 0.96153846,
       1.        , 1.        ], [0.        , 0.03846154, 0.34615385, 0.34615385, 0.42307692,
       0.42307692, 0.61538462, 0.61538462, 0.69230769, 0.69230769,
       0.73076923, 0.73076923, 0.76923077, 0.76923077, 0.80769231,
       0.80769231, 0.84615385, 0.84615385, 0.88461538, 0.88461538,
       0.92307692, 0.92307692, 0.96153846, 0.96153846, 1.        ,
       1.        ], [0.        , 0.03846154, 0.42307692, 0.42307692, 0.57692308,
       0.57692308, 0.76923077, 0.76923077, 0.84615385, 0.84615385,
       0.88461538, 0.88461538, 0.92307692, 0.92307692, 0.96153846,
       0.96153846, 1.        , 1.        ]]


I am trying to compute the mean of this list of list. I am using the following code. 

mean_a=[float(sum(col))/len(col) for col in zip(*a)]


But I am getting the following output.

 0.03846154,
 0.43269231,
 0.43269231,
 0.5288461525,
 0.5288461525,
 0.66346154,
 0.66346154,
 0.7307692325,
 0.7307692325,
 0.7692307675,
 0.7692307675,
 0.8173076925,
 0.8173076925,
 0.8557692299999999,
 0.8557692299999999,
 0.89423077,
 0.89423077]


As you can see the output is wrong as the all the last elements of each list is 1 and so the mean should be 1. But I am getting a different mean for the last element.
I think the number of elements in each lists are different. (26 , 22 , 26 , 18)

Zip() function uniformly maps all elements of lists of same sizes. (And that's why the 1's are missing and would round off to 18 elements)

Try maintaining the same number of elements in each List and try to find the mean again.