ENH: Better emulate Python 3.3+ shutil.which

Author: effigies

nipype/interfaces/base/core.py

@@ -989,7 +989,10 @@ def _run_interface(self, runtime, correct_return_codes=(0, )):
 
         # which $cmd
         executable_name = shlex.split(self._cmd_prefix + self.cmd)[0]
-        cmd_path = which(executable_name, env=runtime.environ)
+        if os.path.isfile(executable_name):
+            cmd_path = executable_name
+        else:
+            cmd_path = which(executable_name, env=runtime.environ)
 
         if cmd_path is None:
             raise IOError(

nipype/utils/filemanip.py

@@ -774,12 +774,20 @@ def which(cmd, env=None, pathext=None):
                 return filename
         return None
 
+    def isexec(path):
+        return os.path.isfile(path) and os.access(path, os.X_OK)
+
     for ext in pathext:
         extcmd = cmd + ext
-        for directory in path.split(os.pathsep):
-            filename = op.join(directory, extcmd)
-            if op.exists(filename):
-                return filename
+        fpath, fname = os.path.split(extcmd)
+        if fpath:
+            if isexec(fpath):
+                return extcmd
+        else:
+            for directory in path.split(os.pathsep):
+                filename = op.join(directory, extcmd)
+                if isexec(filename):
+                    return filename
     return None