Add option for inhibiting the core build while installing the python components. Add option for loading the core from a custom path. (#1089)

bindings/python/README.txt

@@ -8,10 +8,18 @@ compile C code. On Linux, this is usually easy, but on Windows, this involves
 installing Visual Studio and using the "Developer Command Prompt" to perform the
 installation. See BUILDING.txt for more information.
 
+By default, attempting to install the python bindings will trigger a build of
+the capstone native core. If this is undesirable for whatever reason, for
+instance, you already have a globally installed copy of libcapstone, you may
+inhibit the build by setting the environment variable LIBCAPSTONE_PATH. The
+exact value is not checked, just setting it will inhibit the build. During
+execution, this variable may be set to the path of a directory containing a
+specific version of libcapstone you would like to use.
+
 If you don't want to build your own copy of Capstone, you can use a precompiled
 binary distribution from PyPI. Saying `pip install capstone` should
 automatically obtain an appropriate copy for your system. If it does not, please
-open an issue at https://github.com/aquynh/capstone and tag @rhelmot - they
+open an issue at https://github.com/aquynh/capstone and tag @rhelmot - she
 will fix this, probably!
 
 --------------------------------------------------------------------------------

bindings/python/capstone/__init__.py

@@ -230,19 +230,22 @@ def _load_lib(path):
 _cs = None
 
 # Loading attempts, in order
+# - user-provided environment variable
 # - pkg_resources can get us the path to the local libraries
 # - we can get the path to the local libraries by parsing our filename
 # - global load
 # - python's lib directory
 # - last-gasp attempt at some hardcoded paths on darwin and linux
 
-_path_list = [pkg_resources.resource_filename(__name__, 'lib'),
+_path_list = [os.getenv('LIBCAPSTONE_PATH', None),
+              pkg_resources.resource_filename(__name__, 'lib'),
               join(split(__file__)[0], 'lib'),
               '',
               distutils.sysconfig.get_python_lib(),
               "/usr/local/lib/" if sys.platform == 'darwin' else '/usr/lib64']
 
 for _path in _path_list:
+    if _path is None: continue
     _cs = _load_lib(_path)
     if _cs is not None: break
 else:

bindings/python/setup.py

@@ -156,8 +156,11 @@ class custom_sdist(sdist):
 
 class custom_build(build):
     def run(self):
-        log.info('Building C extensions')
-        build_libraries()
+        if 'LIBCAPSTONE_PATH' in os.environ:
+            log.info('Skipping building C extensions since LIBCAPSTONE_PATH is set')
+        else:
+            log.info('Building C extensions')
+            build_libraries()
         return build.run(self)