title: "TypeError: 'Model' object is not callable" when trying to build a basic model using pymc3
body: <p>I'm having trouble getting a basic example using the pymc3 package to run.  the example comes from <a href="https://towardsdatascience.com/markov-chain-monte-carlo-in-python-44f7e609be98" rel="nofollow noreferrer">this</a> tutorial on building Markov Chain Monte Carlo models using python.</p>
  
  <p>When I get to any loop that attempts to build a model, I get an error that reads:  TypeError: 'Model' object is not callable.</p>
  
  <p>Here is an example:</p>
  
  <pre><code>import pymc3 as pm
  with pm.Model() as model:
      x = pm.Data('x', [1., 2., 3.])
      y = pm.Data('y', [1., 2., 3.])
      beta = pm.Normal('beta', 0, 1)
      obs = pm.Normal('obs', x * beta, 1, observed=y)
      trace = pm.sample(1000, tune=1000)
  </code></pre>
  
  <p>I'm using Python version 3.7 and the most current version of pymc3 (and all dependencies).  I realize that this is a really basic error and I appreciate any help anybody can offer.  </p>
  
  <p>Here is the complete stack trace of the error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Program Files\Python37\Lib\site-packages\IPython\core\interactiveshell.py", line 2961, in run_code
      exec(code_obj, self.user_global_ns, self.user_ns)
    File "&lt;ipython-input-76-847c37ac79c2&gt;", line 2, in &lt;module&gt;
      with pm.Model() as model:
  TypeError: 'Model' object is not callable
  </code></pre>