[issue10176] telnetlib.Telnet.read_very_eager() performance

[ptz]

ptz ppt...@gmail.com added the comment:

As David suggested, it indeed seems to be a case of timing. When 
telnetlib.Telnet(...) returns, the server still doesn't have the data cooked, 
and read_very_eager() fetches nothing. So nothing here fails as such, it's just 
that my 0 experience in network programming showed.

Either way, some things you could do to get the function g() above to fetch the 
data the server usually returns upon connection are:

a) insert a time.sleep(t) line after creating the socket. But I don't think 
there is one answer as to what the value of t should be.
b) if one knows the format of the data that will be received, one could use 
read_until(expected string)
c) one could write something like

 def g():
...   f = telnetlib.Telnet(chessclub.com)
...   data = ''
...   while not data:
... data = f.read_some()
...   print data,f.read_very_eager()
...


This simply loops until the server has some cooked data available, then fetches 
it. Tested, works, and is probably the way to do it.

Either way, like David wisely said, this isn't an issue with either Python or 
telnetlib. However, it may be a good idea to add a warning to the documentation 
to the effect that by the time the Telnet constructor returns cooked data is 
typically not yet available from the server. To a beginner network programmer, 
this is far from obvious.

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[issue10176] telnetlib.Telnet.read_very_eager() performance

[Jack Diederich]

Jack Diederich jackd...@gmail.com added the comment:

There was no test suite for telnetlib prior to 2.7/3.1 so it is easily possible 
that this is a regression.  If you can post a test case that fails or - even 
better - a patch that passes where the current code fails I'd be very 
appreciative.

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[issue10176] telnetlib.Telnet.read_very_eager() performance

[ptz]

New submission from ptz ppt...@gmail.com:

In Python 2.4, Assuming we've imported telnetlib, the following works:

 f = telnetlib.Telnet(some_text_based_server)
 f.read_very_eager()

The last call outputs the text that the server outputs upon connection (e.g. 
login: ).

However, if we put this inside a function it does not work:

 def g():
...   f = telnetlib.Telnet(server)
...   data = f.read_very_eager()
...   print data
...
 g()

This returns the empty string. I believe this indicates that the data from the 
server isn't cooked. 

Note that if we use read_until() instead of read_very_eager(), everything works 
as expected, further supporting the hypothesis that data doesn't cook properly 
when the functions are called as above.

So why the difference?

--
components: Library (Lib)
messages: 119423
nosy: ptz
priority: normal
severity: normal
status: open
title: telnetlib.Telnet.read_very_eager() performance
type: behavior
versions: 3rd party

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[issue10176] telnetlib.Telnet.read_very_eager() performance

[R. David Murray]

R. David Murray rdmur...@bitdance.com added the comment:

Presumably the difference is that there is a pause between the two statement 
executions at the interactive prompt (even if you cut and paste) that does not 
exist in the function.

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nosy: +r.david.murray
resolution:  - invalid
stage:  - committed/rejected
status: open - closed

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[issue10176] telnetlib.Telnet.read_very_eager() performance

[ptz]

ptz ppt...@gmail.com added the comment:

Strange. I was certain that I tried inserting a time.sleep() in the function 
and it still didn't work, but I tried it just now and it does work as expected. 
Sorry, and thanks for your answer, at least I learned something.

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[issue10176] telnetlib.Telnet.read_very_eager() performance

[R. David Murray]

R. David Murray rdmur...@bitdance.com added the comment:

Well, perhaps when you ran the test with the sleep the target server had an 
unusually long startup delay.  If you are going to use read_very_eager you are 
going to have to deal with the possibility of not getting back what you 
expected, so it doesn't really matter what it's performance is :)

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