Add to_pymc method to distributions (#523)

* add to_pymc method

* add to_pymc method

preliz/distributions/distributions.py

@@ -2,6 +2,7 @@
 Parent classes for all families.
 """
 # pylint: disable=no-member
+# pylint: disable=import-outside-toplevel
 from collections import namedtuple
 from copy import copy
 
@@ -257,6 +258,36 @@ def hdi(self, mass=0.94, fmt=".2f"):
         else:
             return None
 
+    def to_pymc(self, name=None, **kwargs):
+        """
+        Convert the PreliZ distribution to a PyMC distribution.
+
+        name : str
+            Name of PyMC distribution. Needed if inside Model context
+        kwargs : PyMC distributions properties
+            kwargs are used to specify properties such as shape or dims
+
+        Returns
+        -------
+        PyMC distribution
+        """
+        try:
+            import pymc.distributions as pm_dists
+            from pymc.model import Model
+
+            model = Model.get_context(error_if_none=False)
+
+            if model is None:
+                return getattr(pm_dists, self.__class__.__name__).dist(**self.params_dict, **kwargs)
+            else:
+                return getattr(pm_dists, self.__class__.__name__)(
+                    name, **self.params_dict, **kwargs
+                )
+        except ImportError:
+            pass
+
+        return None
+
     def _check_endpoints(self, lower, upper, raise_error=True):
         """
         Evaluate if the lower and upper values are in the support of the distribution

preliz/tests/test_distributions.py

@@ -1,6 +1,7 @@
 # pylint: disable=redefined-outer-name
 
 import pytest
+from pymc import Model
 from numpy.testing import assert_almost_equal
 import numpy as np
 from test_helper import run_notebook
@@ -293,3 +294,12 @@ def test_plot_interactive(capsys, a_few_poissons):
     captured = capsys.readouterr()
     assert "RuntimeError" in captured.out
     run_notebook("plot_interactive.ipynb")
+
+
+def test_to_pymc():
+    with Model() as model:
+        Gamma(1, 1).to_pymc("a", shape=(2, 2))
+
+    assert model.basic_RVs[0].name == "a"
+    assert model.basic_RVs[0].ndim == 2
+    assert Normal(0, 1).to_pymc(shape=2).ndim == 1