Using __repr__ or __str__ for own printable class?

Steven Taschuk staschuk at telusplanet.net
Sat Apr 26 00:39:01 CEST 2003


Quoth I:
  [...]
> ... How about this?  (Draft.)
> 
> __repr__(self)
> 
>     Called by the repr() built-in function and by string conversions
  [...]

I've submitted a documentation patch for the __str__ and __repr__
docs, following ideas discussed in this thread:
    <http://www.python.org/sf/727789>
I solicit comments.  (The __repr__ blurb is much the same as that
in the previous post; I've fiddled more extensively with the
__str__ blurb.)

__repr__(self)

    Called by the repr() built-in function and by string conversions
    (reverse quotes) to compute a string representation of an object.
    The return value must be a string object.

    The primary audience of this representation is programmers seeking
    detailed information about the object for debugging or inspection
    purposes; thus it is important that the representation be
    information-rich and unambiguous.  This representation should not
    usually be parsed or manipulated by other code.

    In some cases the best information-rich and unambiguous
    representation is a Python expression which evaluates to the
    object, that is, for eval(repr(x)) to return an object which is
    equal to x (given an appropriate environment).  For example, the
    built-in numeric types all have such __repr__() implementations,
    as do the built-in sequence and mapping types (except for cases in
    which a container contains itself).  Where such a representation
    is infeasible or undesirable, this method should return a string
    of the form <...some useful description...>.

    If a class defines __repr__() but not __str__(), then __repr__()
    is also used when __str__() would otherwise be called.

__str__(self)

    Called by the str() built-in function and by the print statement
    to compute a string representation of an object.  The return value
    must be a string object.

    This differs from __repr__() in that it does not specifically
    serve the purpose of providing a programmer with detailed
    information about the object; it may provide a string
    representation of the object for other purposes, as appropriate to
    the object.  Such purposes include display to an application
    end-user, reference in an application log for administrators, or
    providing a string to other code which requires one -- in general,
    purposes for which the programmer-oriented information of
    __repr__() is not appropriate.

-- 
Steven Taschuk                            staschuk at telusplanet.net
Every public frenzy produces legislation purporting to address it.
                                                  (Kinsley's Law)





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