Sorry, but I Just Don't Get It. I did search the 'net, I did read the
FAQ, but I'm too dumb to understand.
As far as I can gather, __str__ is just a representation of the
object. For instance:
class ServerConnectio n:
def __str__(self):
buf = "Server: " + self.name + "\n"
buf += "Sent bytes: " + str(self.sentBy tes) + "\n"
buf += "Recv bytes: " + str(self.recvBy tes) + "\n"
return buf
However, I don't understand what __repr__ should be. There's a phrase
in the documentation which makes it highly confusing for a beginner like
me: "If at all possible, this should look like a valid Python expression
that could be used to recreate an object with the same value (given an
appropriate environment).". What does that mean? Does it mean that I
should return:
def __str__(self):
buf = "self.name= " + self.name + "\n"
buf += "self.sentBytes =" + str(self.sentBy tes) + "\n"
buf += "self.recvBytes =" + str(self.recvBy tes) + "\n"
return buf
..or is there some other "valid Python expression" format which I
have yet to encounter?
Jul 19 '05
15  2940 
Quoth "John Roth" <ne********@jhr othjr.com>:
....
| str() should be something that's meaningful to a human being when
| it's printed or otherwise rendered.
I can't believe how many people cite this explanation - meaningful,
friendly, pretty to a human being. What on earth does this mean,
that couldn't be said more unambiguously?
According to my impression of common applications for Python programs,
rarely would anyone be looking at the output for esthetic gratification.
I mean, imagine your users casting an appraising eye over the contours
of a phrase emitted by the program, and praising the rhythmic effect of
the punctuation it chose to use, or negative space created by tabs. heh.
Whether for human eyes or any destination, properly formed output will
carry the information that is required for the application, in a complete
and unambiguous way and in the format that is most readily processed,
and it will omit extraneous information. Are we saying anything other
than this?
Donn Cave, do**@drizzle.co m
"Donn Cave" <do**@drizzle.c om> wrote in message
news:1118898421 .887013@yasure. .. Quoth "John Roth" <ne********@jhr othjr.com>:
...
| str() should be something that's meaningful to a human being when
| it's printed or otherwise rendered.
I can't believe how many people cite this explanation - meaningful,
friendly, pretty to a human being. What on earth does this mean,
that couldn't be said more unambiguously?
According to my impression of common applications for Python programs,
rarely would anyone be looking at the output for esthetic gratification.
I mean, imagine your users casting an appraising eye over the contours
of a phrase emitted by the program, and praising the rhythmic effect of
the punctuation it chose to use, or negative space created by tabs. heh.
Whether for human eyes or any destination, properly formed output will
carry the information that is required for the application, in a complete
and unambiguous way and in the format that is most readily processed,
and it will omit extraneous information. Are we saying anything other
than this?
I thought that's what I said. I fail to see how you derive any other
meaning from it. Possibly less verbiage and a concerete example
of how "meaningful " equates to "esthetics that obfustificate understanding"
and does not equate to "immediatel y useable, without having to wade
through a lot of irrelvant mental transformations " would help my
understanding.
John Roth
Donn Cave, do**@drizzle.co m
In article <11************ *@news.supernew s.com>,
"John Roth" <ne********@jhr othjr.com> wrote: "Donn Cave" <do**@drizzle.c om> wrote in message
news:1118898421 .887013@yasure. .. Quoth "John Roth" <ne********@jhr othjr.com>:
...
| str() should be something that's meaningful to a human being when
| it's printed or otherwise rendered.
I can't believe how many people cite this explanation - meaningful,
friendly, pretty to a human being. What on earth does this mean,
that couldn't be said more unambiguously?
According to my impression of common applications for Python programs,
rarely would anyone be looking at the output for esthetic gratification.
I mean, imagine your users casting an appraising eye over the contours
of a phrase emitted by the program, and praising the rhythmic effect of
the punctuation it chose to use, or negative space created by tabs. heh.
Whether for human eyes or any destination, properly formed output will
carry the information that is required for the application, in a complete
and unambiguous way and in the format that is most readily processed,
and it will omit extraneous information. Are we saying anything other
than this?
I thought that's what I said. I fail to see how you derive any other
meaning from it. Possibly less verbiage and a concerete example
of how "meaningful " equates to "esthetics that obfustificate understanding"
and does not equate to "immediatel y useable, without having to wade
through a lot of irrelvant mental transformations " would help my
understanding.
Not sure if that's a question. Maybe I can state this more clearly.
Observation: Most who responded to this question offered an
explanation of __str__ like "friendly to a human being",
using one or more of meaningful, friendly or pretty. The
online manual uses "informal".
1. These words are woefully ambiguous, to be applied in computer
programming. While there may be some kind of absolute basis
for esthetic appreciation, that clearly doesn't apply here,
and terms like this have to be strictly relative to context
created by the application.
Summary: By itself, friendly to a human being is a vacuous
notion and doesn't help anyone.
2. If we attempt to support the explanation with a more rigorous
examination of the principles and how they'd apply to a string
conversion, it's hard to make this come out favoring str over
repr. In the end, they should both be meaningful and friendly,
by any uncontorted definition of those terms.
Summary: To the extent that they have any meaning, they are
probably applied incorrectly as an explanation of __str__.
So, among other conclusions, the documentation should be changed
to offer a more sensible explanation of __str__.
Donn Cave, do**@u.washingt on.edu
On 6/15/05, Peter Hansen <pe***@engcorp. com> wrote: __repr__ shouldn't be anything, if you don't have an actual need for it.
Neither should __str__.
Oh, I don't know. __str__ is so frequently useful in debugging and
logging that I always try and do something useful with it.
--
Cheers,
Simon B, si***@brunningo nline.net, http://www.brunningonline.net/simon/blog/
Simon Brunning wrote: On 6/15/05, Peter Hansen <pe***@engcorp. com> wrote:__repr__ shouldn't be anything, if you don't have an actual need for it.
Neither should __str__.
Oh, I don't know. __str__ is so frequently useful in debugging and
logging that I always try and do something useful with it.
Interesting: for the same purpose, I would define __repr__.
But I still define it only when I actually care about the details, since
otherwise the default __repr__ is always there. Spending time figuring
out a potentially more useful __str__/__repr__ (how nice that we've
confused the issue of which to use, again! ;-) ) is not my idea of a
good use of time, what with YAGNI and all from XP...
-Peter __repr__ shouldn't be anything, if you don't have an actual need for
it. Neither should __str__.
Simon> Oh, I don't know. __str__ is so frequently useful in debugging
Simon> and logging that I always try and do something useful with it.
And sometimes __repr__ inherited from a base class doesn't tell you much.
If you inherit from gobject (the basic object in PyGtk), the repr is
something like
<Future object (__main__+Base) at 0x851384c>
That is, it identifies the class name, its inheritance hierarchy (Future ->
Base -> __main__ in this case) and its memory address. That's perhaps
useful by itself in some contexts, and I can understand that the PyGtk folks
couldn't really stuff more specific info in there, but it does nothing to
distinguish one instance's state from that of another.
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