Using six.raise_from wherever possible.

google/auth/_default.py

@@ -22,6 +22,8 @@
 import logging
 import os
 
+import six
+
 from google.auth import environment_vars
 from google.auth import exceptions
 import google.auth.transport._http_client
@@ -67,9 +69,11 @@ def _load_credentials_from_file(filename):
     with io.open(filename, 'r') as file_obj:
         try:
             info = json.load(file_obj)
-        except ValueError as exc:
-            raise exceptions.DefaultCredentialsError(
-                'File {} is not a valid json file.'.format(filename), exc)
+        except ValueError as caught_exc:
+            new_exc = exceptions.DefaultCredentialsError(
+                'File {} is not a valid json file.'.format(filename),
+                caught_exc)
+            six.raise_from(new_exc, caught_exc)
 
     # The type key should indicate that the file is either a service account
     # credentials file or an authorized user credentials file.
@@ -80,10 +84,11 @@ def _load_credentials_from_file(filename):
 
         try:
             credentials = _cloud_sdk.load_authorized_user_credentials(info)
-        except ValueError as exc:
-            raise exceptions.DefaultCredentialsError(
-                'Failed to load authorized user credentials from {}'.format(
-                    filename), exc)
+        except ValueError as caught_exc:
+            msg = 'Failed to load authorized user credentials from {}'.format(
+                filename)
+            new_exc = exceptions.DefaultCredentialsError(msg, caught_exc)
+            six.raise_from(new_exc, caught_exc)
         # Authorized user credentials do not contain the project ID.
         return credentials, None
 
@@ -93,10 +98,11 @@ def _load_credentials_from_file(filename):
         try:
             credentials = (
                 service_account.Credentials.from_service_account_info(info))
-        except ValueError as exc:
-            raise exceptions.DefaultCredentialsError(
-                'Failed to load service account credentials from {}'.format(
-                    filename), exc)
+        except ValueError as caught_exc:
+            msg = 'Failed to load service account credentials from {}'.format(
+                filename)
+            new_exc = exceptions.DefaultCredentialsError(msg, caught_exc)
+            six.raise_from(new_exc, caught_exc)
         return credentials, info.get('project_id')
 
     else:

google/auth/_oauth2client.py

@@ -21,6 +21,8 @@
 
 from __future__ import absolute_import
 
+import six
+
 from google.auth import _helpers
 import google.auth.app_engine
 import google.oauth2.credentials
@@ -30,8 +32,9 @@
     import oauth2client.client
     import oauth2client.contrib.gce
     import oauth2client.service_account
-except ImportError:
-    raise ImportError('oauth2client is not installed.')
+except ImportError as caught_exc:
+    six.raise_from(
+        ImportError('oauth2client is not installed.'), caught_exc)
 
 try:
     import oauth2client.contrib.appengine
@@ -162,5 +165,6 @@ def convert(credentials):
 
     try:
         return _CLASS_CONVERSION_MAP[credentials_class](credentials)
-    except KeyError:
-        raise ValueError(_CONVERT_ERROR_TMPL.format(credentials_class))
+    except KeyError as caught_exc:
+        new_exc = ValueError(_CONVERT_ERROR_TMPL.format(credentials_class))
+        six.raise_from(new_exc, caught_exc)

google/auth/compute_engine/_metadata.py

@@ -22,6 +22,7 @@
 import logging
 import os
 
+import six
 from six.moves import http_client
 from six.moves.urllib import parse as urlparse
 
@@ -118,10 +119,11 @@ def get(request, path, root=_METADATA_ROOT, recursive=False):
         if response.headers['content-type'] == 'application/json':
             try:
                 return json.loads(content)
-            except ValueError:
-                raise exceptions.TransportError(
+            except ValueError as caught_exc:
+                new_exc = exceptions.TransportError(
                     'Received invalid JSON from the Google Compute Engine'
                     'metadata service: {:.20}'.format(content))
+                six.raise_from(new_exc, caught_exc)
         else:
             return content
     else:

google/auth/compute_engine/credentials.py

@@ -19,6 +19,8 @@
 
 """
 
+import six
+
 from google.auth import credentials
 from google.auth import exceptions
 from google.auth.compute_engine import _metadata
@@ -89,8 +91,9 @@ def refresh(self, request):
             self.token, self.expiry = _metadata.get_service_account_token(
                 request,
                 service_account=self._service_account_email)
-        except exceptions.TransportError as exc:
-            raise exceptions.RefreshError(exc)
+        except exceptions.TransportError as caught_exc:
+            new_exc = exceptions.RefreshError(caught_exc)
+            six.raise_from(new_exc, caught_exc)
 
     @property
     def service_account_email(self):

google/auth/jwt.py

@@ -47,6 +47,7 @@
 import json
 
 import cachetools
+import six
 from six.moves import urllib
 
 from google.auth import _helpers
@@ -101,8 +102,9 @@ def _decode_jwt_segment(encoded_section):
     section_bytes = _helpers.padded_urlsafe_b64decode(encoded_section)
     try:
         return json.loads(section_bytes.decode('utf-8'))
-    except ValueError:
-        raise ValueError('Can\'t parse segment: {0}'.format(section_bytes))
+    except ValueError as caught_exc:
+        new_exc = ValueError('Can\'t parse segment: {0}'.format(section_bytes))
+        six.raise_from(new_exc, caught_exc)
 
 
 def _unverified_decode(token):

google/auth/transport/_http_client.py

@@ -17,6 +17,7 @@
 import logging
 import socket
 
+import six
 from six.moves import http_client
 from six.moves import urllib
 
@@ -104,8 +105,9 @@ def __call__(self, url, method='GET', body=None, headers=None,
             response = connection.getresponse()
             return Response(response)
 
-        except (http_client.HTTPException, socket.error) as exc:
-            raise exceptions.TransportError(exc)
+        except (http_client.HTTPException, socket.error) as caught_exc:
+            new_exc = exceptions.TransportError(caught_exc)
+            six.raise_from(new_exc, caught_exc)
 
         finally:
             connection.close()

google/auth/transport/grpc.py

@@ -16,13 +16,17 @@
 
 from __future__ import absolute_import
 
+import six
 try:
     import grpc
-except ImportError:  # pragma: NO COVER
-    raise ImportError(
-        'gRPC is not installed, please install the grpcio package to use the '
-        'gRPC transport.')
-import six
+except ImportError as caught_exc:  # pragma: NO COVER
+    six.raise_from(
+        ImportError(
+            'gRPC is not installed, please install the grpcio package '
+            'to use the gRPC transport.'
+        ),
+        caught_exc,
+    )
 
 
 class AuthMetadataPlugin(grpc.AuthMetadataPlugin):

google/auth/transport/requests.py

@@ -20,11 +20,17 @@
 
 try:
     import requests
-except ImportError:  # pragma: NO COVER
-    raise ImportError(
-        'The requests library is not installed, please install the requests '
-        'package to use the requests transport.')
-import requests.exceptions
+except ImportError as caught_exc:  # pragma: NO COVER
+    import six
+    six.raise_from(
+        ImportError(
+            'The requests library is not installed, please install the '
+            'requests package to use the requests transport.'
+        ),
+        caught_exc,
+    )
+import requests.exceptions  # pylint: disable=ungrouped-imports
+import six  # pylint: disable=ungrouped-imports
 
 from google.auth import exceptions
 from google.auth import transport
@@ -111,8 +117,9 @@ def __call__(self, url, method='GET', body=None, headers=None,
                 method, url, data=body, headers=headers, timeout=timeout,
                 **kwargs)
             return _Response(response)
-        except requests.exceptions.RequestException as exc:
-            raise exceptions.TransportError(exc)
+        except requests.exceptions.RequestException as caught_exc:
+            new_exc = exceptions.TransportError(caught_exc)
+            six.raise_from(new_exc, caught_exc)
 
 
 class AuthorizedSession(requests.Session):

google/auth/transport/urllib3.py

@@ -32,11 +32,17 @@
 
 try:
     import urllib3
-except ImportError:  # pragma: NO COVER
-    raise ImportError(
-        'The urllib3 library is not installed, please install the urllib3 '
-        'package to use the urllib3 transport.')
-import urllib3.exceptions
+except ImportError as caught_exc:  # pragma: NO COVER
+    import six
+    six.raise_from(
+        ImportError(
+            'The urllib3 library is not installed, please install the '
+            'urllib3 package to use the urllib3 transport.'
+        ),
+        caught_exc,
+    )
+import six
+import urllib3.exceptions  # pylint: disable=ungrouped-imports
 
 from google.auth import exceptions
 from google.auth import transport
@@ -126,8 +132,9 @@ def __call__(self, url, method='GET', body=None, headers=None,
             response = self.http.request(
                 method, url, body=body, headers=headers, **kwargs)
             return _Response(response)
-        except urllib3.exceptions.HTTPError as exc:
-            raise exceptions.TransportError(exc)
+        except urllib3.exceptions.HTTPError as caught_exc:
+            new_exc = exceptions.TransportError(caught_exc)
+            six.raise_from(new_exc, caught_exc)
 
 
 def _make_default_http():

google/oauth2/_client.py

@@ -26,6 +26,7 @@
 import datetime
 import json
 
+import six
 from six.moves import http_client
 from six.moves import urllib
 
@@ -144,9 +145,10 @@ def jwt_grant(request, token_uri, assertion):
 
     try:
         access_token = response_data['access_token']
-    except KeyError:
-        raise exceptions.RefreshError(
+    except KeyError as caught_exc:
+        new_exc = exceptions.RefreshError(
             'No access token in response.', response_data)
+        six.raise_from(new_exc, caught_exc)
 
     expiry = _parse_expiry(response_data)
 
@@ -190,9 +192,10 @@ def refresh_grant(request, token_uri, refresh_token, client_id, client_secret):
 
     try:
         access_token = response_data['access_token']
-    except KeyError:
-        raise exceptions.RefreshError(
+    except KeyError as caught_exc:
+        new_exc = exceptions.RefreshError(
             'No access token in response.', response_data)
+        six.raise_from(new_exc, caught_exc)
 
     refresh_token = response_data.get('refresh_token', refresh_token)
     expiry = _parse_expiry(response_data)