feat: Add backend option to pyhf CLI

docs/faq.rst

@@ -9,10 +9,10 @@ Questions
 Is it possible to set the backend from the CLI?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Not at the moment. `Pull Requests <https://github.com/scikit-hep/pyhf/compare>`__ are welcome.
-
-See also:
-  - :issue:`266`
+Yes.
+Use the :code:`--backend` option for :code:`pyhf cls` to specify a tensor backend.
+The default backend is NumPy.
+For more information see :code:`pyhf cls --help`.
 
 Troubleshooting
 ---------------

src/pyhf/cli/stats.py

@@ -5,7 +5,7 @@
 
 from ..utils import hypotest, EqDelimStringParamType
 from ..workspace import Workspace
-from .. import tensorlib, set_backend, optimize
+from .. import tensor, get_backend, set_backend, optimize
 
 logging.basicConfig()
 log = logging.getLogger(__name__)
@@ -27,10 +27,24 @@ def cli():
 @click.option('-p', '--patch', multiple=True)
 @click.option('--testpoi', default=1.0)
 @click.option('--teststat', type=click.Choice(['q', 'qtilde']), default='qtilde')
+@click.option(
+    '--backend',
+    type=click.Choice(['numpy', 'pytorch', 'tensorflow', 'np', 'torch', 'tf']),
+    help='The tensor backend used for the calculation.',
+    default='numpy',
+)
 @click.option('--optimizer')
 @click.option('--optconf', type=EqDelimStringParamType(), multiple=True)
 def cls(
-    workspace, output_file, measurement, patch, testpoi, teststat, optimizer, optconf
+    workspace,
+    output_file,
+    measurement,
+    patch,
+    testpoi,
+    teststat,
+    backend,
+    optimizer,
+    optconf,
 ):
     with click.open_file(workspace, 'r') as specstream:
         spec = json.load(specstream)
@@ -49,6 +63,15 @@ def cls(
         },
     )
 
+    # set the backend if not NumPy
+    if backend in ['pytorch', 'torch']:
+        set_backend(tensor.pytorch_backend())
+    elif backend in ['tensorflow', 'tf']:
+        from tensorflow.compat.v1 import Session
+
+        set_backend(tensor.tensorflow_backend(session=Session()))
+    tensorlib, _ = get_backend()
+
     optconf = {k: v for item in optconf for k, v in item.items()}
 
     # set the new optimizer
@@ -59,7 +82,10 @@ def cls(
     result = hypotest(
         testpoi, ws.data(model), model, qtilde=is_qtilde, return_expected_set=True
     )
-    result = {'CLs_obs': result[0].tolist()[0], 'CLs_exp': result[-1].ravel().tolist()}
+    result = {
+        'CLs_obs': tensorlib.tolist(result[0])[0],
+        'CLs_exp': tensorlib.tolist(tensorlib.reshape(result[-1], [-1])),
+    }
 
     if output_file is None:
         click.echo(json.dumps(result, indent=4, sort_keys=True))

src/pyhf/utils.py

@@ -158,14 +158,22 @@ def pvals_from_teststat(sqrtqmu_v, sqrtqmuA_v, qtilde=False):
         nullval = sqrtqmu_v
         altval = -(sqrtqmuA_v - sqrtqmu_v)
     else:  # qtilde
-        if sqrtqmu_v < sqrtqmuA_v:
+
+        def _true_case():
             nullval = sqrtqmu_v
             altval = -(sqrtqmuA_v - sqrtqmu_v)
-        else:
+            return nullval, altval
+
+        def _false_case():
             qmu = tensorlib.power(sqrtqmu_v, 2)
             qmu_A = tensorlib.power(sqrtqmuA_v, 2)
             nullval = (qmu + qmu_A) / (2 * sqrtqmuA_v)
             altval = (qmu - qmu_A) / (2 * sqrtqmuA_v)
+            return nullval, altval
+
+        nullval, altval = tensorlib.conditional(
+            (sqrtqmu_v < sqrtqmuA_v)[0], _true_case, _false_case
+        )
     CLsb = 1 - tensorlib.normal_cdf(nullval)
     CLb = 1 - tensorlib.normal_cdf(altval)
     CLs = CLsb / CLb

tests/test_scripts.py

@@ -99,6 +99,26 @@ def test_import_prepHistFactory_and_cls(tmpdir, script_runner):
         assert 'CLs_exp' in d
 
 
+@pytest.mark.parametrize(
+    "backend", ["numpy", "tensorflow", "pytorch"],
+)
+def test_cls_backend_option(tmpdir, script_runner, backend):
+    temp = tmpdir.join("parsed_output.json")
+    command = 'pyhf xml2json validation/xmlimport_input/config/example.xml --basedir validation/xmlimport_input/ --output-file {0:s}'.format(
+        temp.strpath
+    )
+    ret = script_runner.run(*shlex.split(command))
+
+    command = 'pyhf cls --backend {0:s} {1:s}'.format(backend, temp.strpath)
+    ret = script_runner.run(*shlex.split(command))
+
+    assert ret.success
+    d = json.loads(ret.stdout)
+    assert d
+    assert 'CLs_obs' in d
+    assert 'CLs_exp' in d
+
+
 def test_import_and_export(tmpdir, script_runner):
     temp = tmpdir.join("parsed_output.json")
     command = 'pyhf xml2json validation/xmlimport_input/config/example.xml --basedir validation/xmlimport_input/ --output-file {0:s}'.format(