title: Why does my lambdify not working when add my own function
body: <p>I created a function and make it usable in my Sympy expression like this:</p>
  
  <pre><code>  def Unit(x):
          if(x != 0):
              return 0
          else:
              return 1
    Unit = Function('Unit')
    x = Symbol('x')
  </code></pre>
  
  <p>My expression:</p>
  
  <pre><code>fx = x ** 2 + Unit(x)
  </code></pre>
  
  <p>But when I run:</p>
  
  <pre><code>lam_f = lambdify(x, fx, modules=["sympy"])
  print(lam_f(-1))
  </code></pre>
  
  <p>It said that my Unit is not defined?
  Can anyone explain where i went wrong?</p>