title: lambdify returns TypeError: _lambdifygenerated() missing 1 required positional argument: 'k'
body: <p>I need to solve an equation numerically (solution must depend on k∈⟨0,1)). Every time I use a function that returns expression or use lambda to define function it returns similar error. Now I tried using lambdify to translate a SymPy expression into an equivalent numeric function, but same error is returned.</p>
  
  <pre><code>from scipy import *
  import sympy as sym
  init_printing()
  
  x,k=symbols("x,k")
  f=(sym.log(x)/sym.log(k))**k-x**(1/sym.atanh(k))
  
  a=lambdify([x,k], f, "scipy")
  (a([0,1]))
  </code></pre>
  
  <pre><code>TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-29-04519472dd5e&gt; in &lt;module&gt;
        7 
        8 a=lambdify([x,k], f, "scipy")
  ----&gt; 9 print(a([0,1]))
  
  TypeError: _lambdifygenerated() missing 1 required positional argument: 'k'
  
  </code></pre>