Implement type checking raise from
New test cases for raise from type checking
Cast super_type from Instance down to Type
Add more raise from statement test cases
Remove unused class in fixtures/exception.py
Semantic analyze from_expr of RaiseStmt
Add raise from type checking
Added parse test for nested tupple assignment
Added semanal error message for assignment to empty tuple
Add type_check_raise() function and remove duplicate code
Change type to Node
Merge pull request #463 from yczhu/raise-from

Implement raise from type checking
Renamed identically named tests
Added tests for assignments from/to (nested) lists
Fixed style issues
Merge pull request #466 from spkersten/nestup248

Assignment to and from nested tuples (or lists)
Fix #307: Method default args can refer to class attributes
Update CREDITS
Merge pull request #468 from spkersten/assign2emptytup

Added semanal error message for assignment to empty tuple
Clean up obsolete code

Remove traces of for loop and generator expression annotations.

Closes #464.