Wrong dividing in python [duplicate]

Question

This question already has answers here:

Why does the division get rounded to an integer? [duplicate] (13 answers)

Closed 9 years ago.

As you can see from watch, l[u][0] must be 0.5, but it returns 0

u = 0
for j in range(n):
    if k == j:
        continue
    l[u][0] = -x[j] / (x[k] - x[j])
    l[u][1] = 1 / (x[k] - x[j])
    u = u + 1

What's wrong with it?

Answer 1

The division is not "wrong". It is integer division (a.k.a. floor division).

When you divide two integers, the result is an integer:

>>> 3/4
0
>>> 4/4
1

When you divide two floating-point numbers (numbers with a fractional part), the result is a float:

>>> 3./4
0.75
>>> 4./4
1.0

Note that this "problem" is confined to Python 2. One of the changes in Python 3 is to make normal division coerce to floats:

>>> 3/4   # Python 3 behavior
0.75

and to require a second operator (also in Python >2.2) to achieve integer division:

>>> 3//4
0