remove site searches in util.loadlib

For a library that does not reside in the system path it may not be sufficient
to load it by its absolute path, as any dependencies that are loaded indirectly
will not be resolved. Instead we must set this path a priori, and can thus
remove any fall-back search logic from util.loadlib.

nutils/util.py

@@ -23,7 +23,7 @@
 """
 
 from . import numeric
-import sys, os, numpy, collections.abc, inspect, functools, operator, numbers, pathlib, ctypes, site, io, contextlib
+import sys, os, numpy, collections.abc, inspect, functools, operator, numbers, pathlib, ctypes, io, contextlib
 
 supports_outdirfd = os.open in os.supports_dir_fd and os.listdir in os.supports_fd
 
@@ -356,9 +356,7 @@ def loadlib(**libname):
   Find and load a dynamic library using :any:`ctypes.CDLL`.  For each
   (supported) platform the name of the library should be specified as a keyword
   argument, including the extension, where the keywords should match the
-  possible values of :any:`sys.platform`.  In addition to the default
-  directories, this function searches :any:`site.PREFIXES` and
-  :func:`site.getuserbase()`.
+  possible values of :any:`sys.platform`.
 
   Example
   -------
@@ -368,29 +366,10 @@ def loadlib(**libname):
       loadlib(linux='libmkl_rt.so', darwin='libmkl_rt.dylib', win32='mkl_rt.dll')
   '''
 
-  if sys.platform not in libname:
-    return
-  libname = libname[sys.platform]
   try:
-    return ctypes.CDLL(libname)
+    return ctypes.CDLL(libname[sys.platform])
   except (OSError, KeyError):
     pass
-  libsubdir = dict(linux='lib', darwin='lib', win32='Library\\bin')[sys.platform]
-  prefixes = list(site.PREFIXES)
-  if hasattr(site, 'getuserbase'):
-    prefixes.append(site.getuserbase())
-  for prefix in prefixes:
-    libdir = os.path.join(prefix, libsubdir)
-    if not os.path.exists(os.path.join(libdir, libname)):
-      continue
-    if sys.platform == 'win32' and libdir not in os.environ.get('PATH', '').split(';'):
-      # Make sure dependencies of `libname` residing in the same directory are
-      # found.
-      os.environ['PATH'] = os.environ.get('PATH', '').rstrip(';')+';'+libdir
-    try:
-      return ctypes.CDLL(os.path.join(libdir, libname))
-    except (OSError, KeyError):
-      pass
 
 def readtext(path):
   '''Read file and return contents