moving rebound to optional dependency

.travis.yml

@@ -9,7 +9,8 @@ env:
         - THEANO_FLAGS=floatX=float64,compute_test_value=off
 cache:
   directories:
-  - "$HOME/.cache/pip"
+    - "$HOME/.theano"
+    - "$HOME/.cache/pip"
 
 stages:
   - name: Housekeeping
@@ -23,7 +24,7 @@ jobs:
       install: skip
       script: ./.ci/travis/update_docs.sh
       after_success: skip
-      if: type != pull_request
+      if: (branch = master) AND (type != pull_request)
     - name: "Style"
       install:
         - python -m pip install -U pip

pyproject.toml

@@ -25,4 +25,4 @@ multi_line_output = 3
 include_trailing_comma = true
 force_grid_wrap = 0
 use_parentheses = true
-known_third_party = ["astropy", "matplotlib", "nbconvert", "nbformat", "numpy", "packaging", "pkg_resources", "pymc3", "pytest", "rebound_pymc3", "scipy", "setuptools", "theano", "tqdm"]
+known_third_party = ["astropy", "matplotlib", "nbconvert", "nbformat", "numpy", "packaging", "pkg_resources", "pymc3", "pytest", "scipy", "setuptools", "theano", "tqdm"]

setup.py

@@ -28,8 +28,8 @@
     "numpy>=1.13.0",
     "pymc3>=3.5",
     "astropy>=3.1",
-    "rebound_pymc3>=0.0.3",
 ]
+EXTRA_REQUIRE = {"nbody": ["rebound_pymc3>=0.0.3"]}
 
 # END PROJECT SPECIFIC
 
@@ -73,6 +73,7 @@ def find_meta(meta, meta_file=read(META_PATH)):
         package_dir={"": "src"},
         include_package_data=True,
         install_requires=INSTALL_REQUIRES,
+        extras_require=EXTRA_REQUIRE,
         classifiers=CLASSIFIERS,
         zip_safe=False,
         options={"bdist_wheel": {"universal": "1"}},

src/exoplanet/orbits/rebound.py

@@ -3,11 +3,15 @@
 __all__ = ["ReboundOrbit"]
 
 import theano.tensor as tt
-from rebound_pymc3.integrate import IntegrateOp as ReboundOp
 
 from .constants import au_per_R_sun, day_per_yr_over_2pi
 from .keplerian import KeplerianOrbit
 
+try:
+    from rebound_pymc3.integrate import IntegrateOp as ReboundOp
+except ImportError:
+    from ..theano_ops.rebound import ReboundOp
+
 
 class ReboundOrbit(KeplerianOrbit):
     """An N-body system powered by the rebound integrator

src/exoplanet/theano_ops/rebound/rebound.py

@@ -2,6 +2,8 @@
 
 __all__ = ["ReboundOp"]
 
+import warnings
+
 import numpy as np
 import theano
 import theano.tensor as tt
@@ -13,6 +15,7 @@ class ReboundOp(gof.Op):
     __props__ = ()
 
     def __init__(self, **rebound_args):
+        warnings.warn("For better performance, install 'rebound_pymc3'")
         self.rebound_args = rebound_args
         super(ReboundOp, self).__init__()