Python列表追加错误

Question

I tried to use append with multiple lists at the same time (in a continual line).

However, it added all the items to all of my lists. Please see the script and result below:

x1=y1=z1=[]
for i in range(1,5):
    x1.append(i)
    y1.append(i*4)
    z1.append(i*10)
print ("\n x1=", x1,"\n y1=", y1,"\n z1=", z1)

Result:

 x1= [1, 4, 10, 2, 8, 20, 3, 12, 30, 4, 16, 40] 
 y1= [1, 4, 10, 2, 8, 20, 3, 12, 30, 4, 16, 40] 
 z1= [1, 4, 10, 2, 8, 20, 3, 12, 30, 4, 16, 40]

Thanks for your comment.

Answer 1

That's because x1 , x2 and x3 binds to the same list. Write x1, x2, x3 = [], [], [] instead of x1 = x2 = x3 = [] .

Answer 2

This is because all your list variables are pointing to the same list.

Initialize your lists as follows instead:

x1 = []
y1 = []
z1 = []

Doing, x1 = y1 causes both these variables to point to the same memory space and so modifying one makes it look like you are modifying all of them when in fact they are all just the same thing

Answer 3

If you are only interested in the output, you can do a more pythonic approach using list comprehensions:

print [i for i in range(1,5)]
print [i*4 for i in range(1,5)]
print [i*10 for i in range(1,5)]

Or if you want to keep the values then do:

x1 = [i for i in range(1,5)]
y1 = [i*4 for i in range(1,5)]
z1 = [i*10 for i in range(1,5)]
print ("\n x1=", x1,"\n y1=", y1,"\n z1=", z1)

Or if you really want to shrink your code, you could do this:

for j in zip(*[[i,i*4,i*10] for i in range(1,5)]): print j