title: 'int' object is not callable error in python
body: <p>I'm getting this error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Users\George\Desktop\ex3.py", line 15, in &lt;module&gt;
      s=s+d*2(-1/6.)*(u-1)*(u-2)*(u+2)*(u-4)
  TypeError: 'int' object is not callable
  </code></pre>
  
  <p>Here is my code:</p>
  
  <pre><code>x=input()
  z=input()
  n=input()
  while x&gt;=z:
      x=input()
      z=input()
  while n&lt;0:
      n=input()
  while n&gt;0:
      d=(z-x)/1.*n
      k=1
      s=(d/2.)*((-1/6.)*(x-1)*(x-2)*(x+2)*(x-4)+(-1/6.)*(z-1)*(z-2)*(z+2)*(z-4))
      while k&lt;=n-1:
          u=x+k*d
          s=s+d*2(-1/6.)*(u-1)*(u-2)*(u+2)*(u-4)
          k=k+1
          print "%.3f" %s
          x=input()
          z=input()
          n=input()
          if n&gt;0:
              while x&gt;=z:
                  x=input()
                  z=input()
  </code></pre>