TypeError: zip argument #1 must support iteration (Vector sum for Ipython)

Question

Hi I'm following "Data Science from Scratch" and I got an error when I was making vector sum function. Could someone help?

The code:

a = [1,2,3]
b = [2,3,4]

def vector_add(v, w):
    """adds two vectors componentwise"""
    return [v_i + w_i for v_i, w_i in zip(v,w)]
vector_add(a,b) #prints [3, 5, 7]

def vector_sum(vectors):
    result = vectors[0]
    for vector in vectors[1:]:
        result = vector_add(result, vector)     
    return result
vector_sum(a)

Error:

TypeError                                 Traceback (most recent call last)
<ipython-input-41-401c63999247> in <module>()
      4         result = vector_add(result, vector)
      5     return result
----> 6 vector_sum(a)

<ipython-input-41-401c63999247> in vector_sum(vectors)
      2     result = vectors[0]
      3     for vector in vectors[1:]:
----> 4         result = vector_add(result, vector)
      5     return result
      6 vector_sum(a)

<ipython-input-15-502c43cd9568> in vector_add(v, w)
      4 def vector_add(v, w):
      5     """adds two vectors componentwise"""
----> 6     return [v_i + w_i for v_i, w_i in zip(v,w)]
      7 vector_add(a,b)

TypeError: zip argument #1 must support iteration

Answer 1

If you do vector_sum(a) the local variable result will be the integer "1" in your first step which is not iterable. So I guess you simply should call your function vector_sum like

vector_sum([a,b,a])

to sum up multiple vectors. Latter gives [4,7,10] on my machine.

If you want to sum up the components of one vector you should not use your vector_add function.