clib: Search and load the GMT library only one time

Author: seisman

pygmt/clib/session.py

@@ -34,6 +34,8 @@
     tempfile_from_image,
 )
 
+__libgmt__ = load_libgmt()
+
 FAMILIES = [
     "GMT_IS_DATASET",  # Entity is a data table
     "GMT_IS_GRID",  # Entity is a grid
@@ -308,7 +310,7 @@ def get_libgmt_func(self, name, argtypes=None, restype=None):
         <class 'ctypes.CDLL.__init__.<locals>._FuncPtr'>
         """
         if not hasattr(self, "_libgmt"):
-            self._libgmt = load_libgmt()
+            self._libgmt = __libgmt__
         function = getattr(self._libgmt, name)
         if argtypes is not None:
             function.argtypes = argtypes