tools/file_import: restore sys.modules. Closes #976

artiq/tools.py

@@ -6,6 +6,7 @@ import collections
 import atexit
 import string
 import os
+from copy import copy
 
 import numpy as np
 
@@ -83,9 +84,13 @@ def file_import(filename, prefix="file_import_"):
 
     path = os.path.dirname(os.path.realpath(filename))
     sys.path.insert(0, path)
+    try:
+        previous_modules = copy(sys.modules)
         try:
             loader = importlib.machinery.SourceFileLoader(modname, filename)
             module = loader.load_module()
+        finally:
+            sys.modules = previous_modules
     finally:
         sys.path.remove(path)