title: Calculating the Derivative of a Function
body: <p>I am brand new to programming and am really struggling to create functions in Python.</p>
  
  <p>While trying to calculate a derivative, I created an np.linspace for my x values and then created an empty list for the y values. I used a for-loop to created a list of y values that are the result of passing the x values through a function. After appending the empty list with the result from the for-loop, a tried to create a function to take the derivative using a finite difference approximation. When I run the program I get an error for <strong>Invalid syntax</strong>.</p>
  
  <p>What am I doing wrong?</p>
  
  <pre><code>import numpy as np
  from math import *
  
  xvalue = np.linspace(0,100,20)
  yvalue = []
  
  for i in xvalue:    
      q = i**2+4
      yvalue.append(q)  
  
  def diff(f,x):
  
      n= len(x)
      y = []
  
      for i in range(n):
  
          if i == n-1:
              y.append((f[i]-f[i-1])/(x[2]-x[1]))
          else:
              y.append((f[i+1]-f[i]/(x[2]-x[1]))
  
      return y
  
  print xvalue
  print yvalue
  
  diff(xvalue,yvalue)
  </code></pre>