flake8 fixes

tests/gpuarray/test_multinomial.py

 import os
-from pickle import Unpickler
 
 import numpy as np
 import pytest
@@ -372,8 +371,3 @@ def test_gpu_opt_wor():
         pval = pval / pval.sum(axis=1)[:, None]
         uval = np.ones_like(pval[:, 0]) * 0.5
         f(pval, uval, 1)
-
-
-def test_unpickle_legacy_op():
-    testfile_dir = os.path.dirname(os.path.realpath(__file__))
-    fname = "test_gpuarray_multinomial_wo_replacement.pkl"

theano/gof/cmodule.py

@@ -1941,7 +1941,7 @@ class Compiler:
         if not compiler:
             return False
 
-        code = b(
+        code = (
             """
         %(preambule)s
         int main(int argc, char** argv)
@@ -1951,7 +1951,7 @@ class Compiler:
         }
         """
             % locals()
-        )
+        ).encode()
         return cls._try_compile_tmp(
             code,
             tmp_prefix="try_flags_",

theano/gof/utils.py

+import hashlib
 import linecache
 import sys
 import traceback
 from io import StringIO
 
-import numpy as np
-
 from theano import config
 
 
@@ -597,9 +596,6 @@ def remove(predicate, coll):
     return [x for x in coll if not predicate(x)]
 
 
-import hashlib
-
-
 def hash_from_code(msg):
     # hashlib.sha256() requires an object that supports buffer interface,
     # but Python 3 (unicode) strings don't.