TypeError: cannot unpack non-iterable int object . When I tried to attend the len of x, it give me an error msg said it is float, now it is int?

Question

I created a function to calculate distance from every two places. x and y are a list of locations x s and y s

def calculate_distances(x,y):
    N=len(str(x))
    a=[[0]*N]*N
    for i,j in range(N):
        a[i][j]=np.sqrt((x[i]-x[j])**2+(y[i]-y[j])**2)
    return a

I applied it in a segment that offered by instructor.

D = calculate_distances(x,y)

fig = plt.figure(figsize=(6,6));
total_distance = 0
for i in range(n_city-1):
    plt.scatter(x,y,marker="s",c="k");
    plt.plot([x[i],x[i+1]], [y[i],y[i+1]],
             alpha=(i+1)/(n_city),lw=2,color="k");
    total_distance += D[i,i+1]
    plt.title("Distance traveled = %0.3f" %total_distance)
    time.sleep(1.0)  
    clear_output(wait = True)
    display(fig) # Reset display

And I received the error msg, I pasted below

TypeError                                 Traceback (most recent call last)
<ipython-input-21-3804c182182f> in <module>
      3 # We use the calculate_distances function you created above to compute the distance matrix
      4 # Make sure you feed in the correct "x" and "y" arrays if you used different variables names
----> 5 D = calculate_distances(x,y)
      6 
      7 fig = plt.figure(figsize=(6,6));

<ipython-input-20-ecc344ee386f> in calculate_distances(x, y)
      3     N=len(str(x))
      4     a=[[0]*N]*N
----> 5     for i,j in range(N):
      6         a[i][j]=np.sqrt((x[i]-x[j])**2+(y[i]-y[j])**2)
      7     return a

TypeError: cannot unpack non-iterable int object```

What do you expect `for i,j in range(N):` to do? `range(N)` only returns one number at a time, you can't assign it to two variables. — Barmar, Apr 07 '21 at 23:26
`a=[[0]*N]*N` is also wrong. See https://stackoverflow.com/questions/240178/list-of-lists-changes-reflected-across-sublists-unexpectedly — Barmar, Apr 07 '21 at 23:27
You need nested loops: `for i in range(N): for j in range(N): ...` — Barmar, Apr 07 '21 at 23:28
If `x` is a list of locations, why are you using `len(str(x))` instead of `len(x)`? — Barmar, Apr 07 '21 at 23:29
I do not know what x is, however, if I use len(x), it give me an error msg kind of told me that I can not use len on float. — guokelsey, Apr 07 '21 at 23:44
If you're getting that error, then `x` is not a list of locations, it's a single location. — Barmar, Apr 07 '21 at 23:45
Like it says in the comment: make sure you feed in the correct x and y arrays. — Barmar, Apr 07 '21 at 23:47

score 0 · Answer 1 · answered Apr 07 '21 at 23:48

range(N) only returns a single sequence of indexes. If you want to iterate over both rows and columns, you can use nested loops.

len(str(x)) should just be len(x), since x and y should be lists of coordinates.

When initializing a, you need to use a list comprehension rather than multiplying [0]*N by N. The latter will make all the rows references to the same list.

def calculate_distances(x,y):
    N=len(x)
    a=[[0]*N for _ in range(N)]
    for i in range(N):
        for j in range(N):
            a[i][j]=np.sqrt((x[i]-x[j])**2+(y[i]-y[j])**2)
    return a

TypeError: cannot unpack non-iterable int object . When I tried to attend the len of x, it give me an error msg said it is float, now it is int?

1 Answers1