docs: fix loading library (#492)

docs/conf.py

@@ -19,14 +19,24 @@
 #
 import os
 import sys
-sys.path.insert(0, os.path.abspath('../python-package'))
+
+curr_path = os.path.dirname(os.path.realpath(__file__))
+libpath = os.path.join(curr_path, '../python-package/')
+sys.path.insert(0, libpath)
 
 from recommonmark.parser import CommonMarkParser
 from recommonmark.transform import AutoStructify
 
+# -- mock out modules
+from unittest.mock import Mock
+MOCK_MODULES = ['numpy', 'scipy', 'scipy.sparse', 'sklearn', 'matplotlib', 'pandas', 'graphviz']
+for mod_name in MOCK_MODULES:
+    sys.modules[mod_name] = Mock()
 
 # -- General configuration ------------------------------------------------
 
+os.environ['LIGHTGBM_BUILD_DOC'] = '1'
+
 # If your documentation needs a minimal Sphinx version, state it here.
 #
 # needs_sphinx = '1.0'

python-package/lightgbm/basic.py

@@ -22,7 +22,7 @@ def _load_lib():
     """Load LightGBM Library."""
     lib_path = find_lib_path()
     if len(lib_path) == 0:
-        raise Exception("cannot find LightGBM library")
+        return None
     lib = ctypes.cdll.LoadLibrary(lib_path[0])
     lib.LGBM_GetLastError.restype = ctypes.c_char_p
     return lib

python-package/lightgbm/libpath.py

@@ -11,6 +11,10 @@ def find_lib_path():
     lib_path: list(string)
        List of all found library path to LightGBM
     """
+    if os.environ.get('LIGHTGBM_BUILD_DOC', False):
+        # we don't need lib_lightgbm while building docs
+        return []
+
     curr_path = os.path.dirname(os.path.abspath(os.path.expanduser(__file__)))
     dll_path = [curr_path, os.path.join(curr_path, '../../lib/'),
                 os.path.join(curr_path, '../../'),