title: Plus and minus sequence in Python
body: <p>im creating a program which sums the values in a sequence, but it has alternate plus/minus.</p>
  
  <p>I want to make the sum of this sequence 1-(1/3)+(1/5)-(1/7)....How can i use an alternate plus and minus just like the previous example?</p>
  
  <p>Here is the code i have made so far:</p>
  
  <pre><code>s=input("Ingrese el numero de terminos a sumar:", )
  
  sum=1.0
  num=1.0
  
  for i in xrange(1,s+1):
      ident=sum/(i+(i+1.0))
      sum=sum+-ident    
  
  print "La suma de los",s,"terminos es %.2f"%(sum)
  </code></pre>