oauth: narrow on exception handling

It is generally not advisable to use "except:" in python, because it would
catch "KeyboardInterrupt" and "SystemExit", meant only to be caught at
main() level. Only catch the ones we really expect to see, let others
propagate up the stack.

Also, when computing the HMAC, we shall not retry w/o hashlib in the case
that first hashing has gone wrong. This confuses the error message between
a missing import and a bad supplied hash.

Author: xrg

oauth/oauth.py

@@ -183,7 +183,7 @@ def set_parameter(self, parameter, value):
     def get_parameter(self, parameter):
         try:
             return self.parameters[parameter]
-        except:
+        except KeyError:
             raise OAuthError('Parameter not found: %s' % parameter)
 
     def _get_timestamp_nonce(self):
@@ -224,7 +224,7 @@ def get_normalized_parameters(self):
         try:
             # Exclude the signature if it exists.
             del params['oauth_signature']
-        except:
+        except KeyError:
             pass
         # Escape key values before sorting.
         key_values = [(escape(_utf8_str(k)), escape(_utf8_str(v))) \
@@ -278,7 +278,7 @@ def from_request(http_method, http_url, headers=None, parameters=None,
                     # Get the parameters from the header.
                     header_params = OAuthRequest._split_header(auth_header)
                     parameters.update(header_params)
-                except:
+                except Exception:
                     raise OAuthError('Unable to parse OAuth parameters from '
                         'Authorization header.')
 
@@ -450,7 +450,7 @@ def _get_version(self, oauth_request):
         """Verify the correct version request for this server."""
         try:
             version = oauth_request.get_parameter('oauth_version')
-        except:
+        except Exception:
             version = VERSION
         if version and version != self.version:
             raise OAuthError('OAuth version %s not supported.' % str(version))
@@ -461,12 +461,12 @@ def _get_signature_method(self, oauth_request):
         try:
             signature_method = oauth_request.get_parameter(
                 'oauth_signature_method')
-        except:
+        except Exception:
             signature_method = SIGNATURE_METHOD
         try:
             # Get the signature method object.
             signature_method = self.signature_methods[signature_method]
-        except:
+        except KeyError:
             signature_method_names = ', '.join(self.signature_methods.keys())
             raise OAuthError('Signature method %s not supported try one of the '
                 'following: %s' % (signature_method, signature_method_names))
@@ -498,7 +498,7 @@ def _check_signature(self, oauth_request, consumer, token):
         signature_method = self._get_signature_method(oauth_request)
         try:
             signature = oauth_request.get_parameter('oauth_signature')
-        except:
+        except Exception:
             raise OAuthError('Missing signature.')
         # Validate the signature.
         valid_sig = signature_method.check_signature(oauth_request, consumer,
@@ -629,7 +629,7 @@ def build_signature(self, oauth_request, consumer, token):
         try:
             import hashlib # 2.5
             hashed = hmac.new(key, raw, hashlib.sha1)
-        except:
+        except ImportError:
             import sha # Deprecated
             hashed = hmac.new(key, raw, sha)