@@ -699,12 +699,12 @@ def _strict_call(self, value):
699699 # We're still here so we can now return the new value
700700 return new_value
701701
702- except ValueError :
702+ except ValueError as e :
703703 if value .strip () in self .missing_values :
704704 if not self ._status :
705705 self ._checked = False
706706 return self .default
707- raise ValueError ("Cannot convert string '%s'" % value )
707+ raise ValueError ("Cannot convert string '%s'" % value ) from e
708708 #
709709
710710 def __call__ (self , value ):
@@ -735,17 +735,17 @@ def upgrade(self, value):
735735 self ._checked = True
736736 try :
737737 return self ._strict_call (value )
738- except ValueError :
738+ except ValueError as e :
739739 # Raise an exception if we locked the converter...
740740 if self ._locked :
741741 errmsg = "Converter is locked and cannot be upgraded"
742- raise ConverterLockError (errmsg )
742+ raise ConverterLockError (errmsg ) from e
743743 _statusmax = len (self ._mapper )
744744 # Complains if we try to upgrade by the maximum
745745 _status = self ._status
746746 if _status == _statusmax :
747747 errmsg = "Could not find a valid conversion function"
748- raise ConverterError (errmsg )
748+ raise ConverterError (errmsg ) from e
749749 elif _status < _statusmax - 1 :
750750 _status += 1
751751 (self .type , self .func , default ) = self ._mapper [_status ]
@@ -764,18 +764,18 @@ def iterupgrade(self, value):
764764 try :
765765 for _m in value :
766766 _strict_call (_m )
767- except ValueError :
767+ except ValueError as e :
768768 # Raise an exception if we locked the converter...
769769 if self ._locked :
770770 errmsg = "Converter is locked and cannot be upgraded"
771- raise ConverterLockError (errmsg )
771+ raise ConverterLockError (errmsg ) from e
772772 _statusmax = len (self ._mapper )
773773 # Complains if we try to upgrade by the maximum
774774 _status = self ._status
775775 if _status == _statusmax :
776776 raise ConverterError (
777777 "Could not find a valid conversion function"
778- )
778+ ) from e
779779 elif _status < _statusmax - 1 :
780780 _status += 1
781781 (self .type , self .func , default ) = self ._mapper [_status ]
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