imports: Handle remaining incompatible imports

Import specific exceptions from urllib3 & requests to be compatible
with vendoring. Also organize imports so tuf internal imports are last.

Signed-off-by: Jussi Kukkonen <[email protected]>

tuf/client/updater.py

@@ -127,8 +127,11 @@
 import time
 import fnmatch
 import copy
+from requests.exceptions import HTTPError
+import six
 import warnings
 
+
 from securesystemslib import exceptions as sslib_exceptions
 from securesystemslib import formats as sslib_formats
 from securesystemslib import hash as sslib_hash
@@ -146,9 +149,6 @@
 from tuf import settings
 from tuf import sig
 
-import six
-import requests.exceptions
-
 # The Timestamp role does not have signed metadata about it; otherwise we
 # would need an infinite regress of metadata. Therefore, we use some
 # default, but sane, upper file length for its metadata.
@@ -1114,7 +1114,7 @@ def _update_root_metadata(self, current_root_metadata):
     """
 
     def neither_403_nor_404(mirror_error):
-      if isinstance(mirror_error, requests.exceptions.HTTPError):
+      if isinstance(mirror_error, HTTPError):
         if mirror_error.response.status_code in {403, 404}:
           return False
       return True

tuf/download.py

@@ -35,20 +35,18 @@
 import time
 import timeit
 import tempfile
-
-import tuf
 import requests
+import six
+from urllib3.exceptions import ReadTimeoutError
 
 import securesystemslib
 from securesystemslib import formats as sslib_formats
-import six
 
+import tuf
 from tuf import exceptions
 from tuf import formats
 from tuf import settings
 
-import urllib3.exceptions
-
 # See 'log.py' to learn how logging is handled in TUF.
 logger = logging.getLogger(__name__)
 
@@ -375,7 +373,7 @@ def _download_fixed_amount_of_data(response, temp_file, required_length):
         # Finally, we signal that the download is complete.
         break
 
-  except urllib3.exceptions.ReadTimeoutError as e:
+  except ReadTimeoutError as e:
     raise exceptions.SlowRetrievalError(str(e))
 
   return number_of_bytes_received, average_download_speed