Default printing behavior for classes

Charles G Waldman cgw at fnal.gov
Thu Jun 24 20:03:26 CEST 1999


You're looking for the __repr__ and/or __str__ methods:

>From the docs:

 __repr__ (self) 
     Called by the repr() built-in function and by string conversions
 (reverse quotes) to compute the ``official'' string representation of
 an object. This should normally look like a valid Python expression
 that can be used to recreate an object with the same value. By
 convention, objects which cannot be trivially converted to strings
 which can be used to create a similar object produce a string of the
 form "<...some useful description...>".

 __str__ (self) 
      Called by the str() built-in function and by the print statement
 to compute the ``informal'' string representation of an object. This
 differs from __repr__() in that it does not have to be a valid Python
 expression: a more convenient or concise representation may be used
 instead.

Note that these methods should *return* the string value, not print
it.

If c is a class instance, and the class has __repr__ or __str__
methods,  these will be invoked when you say "print c".

If you have both a __str__ method and a __repr__ method, the __str__
will be used when you say "print c".  But if you only have a 
__repr__ that will be used.







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