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

artiq/tools.py

@@ -7,6 +7,7 @@ import os
 import atexit
 import string
 import random
+from copy import copy
 
 import numpy as np
 
@@ -85,8 +86,12 @@ def file_import(filename, prefix="file_import_"):
     path = os.path.dirname(os.path.realpath(filename))
     sys.path.insert(0, path)
     try:
-        loader = importlib.machinery.SourceFileLoader(modname, filename)
-        module = loader.load_module()
+        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)