[Tutor] Tutor Digest, Vol 139, Issue 29 Calling instance method in IDLE magically calls __len__?

[Dino Bektešević]

Hello all,

Hi Dino,
I'm afraid I cannot replicate that behaviour. Also the output seems
strange -- the "len is called" is printed on the same line as the
prompt, and e.toFile( afterwards.
If you quit idle and restart it, do you get the same behaviour? What's
the exact version of Python?
import sys
print sys.version
--
Steve

The exact version is 2.7.6 (2.7.6 (default, Jun 22 2015, 17:58:13) [GCC
4.8.2])
The behaviour is replicable even after OS restarts. As you've noticed the
print statement gets executed and pushes the typing command into a
new-line, this behaviour is not replicable when the file is imported as a
module or run the terminal.

I have tried figuring out what was happening by using the inspect module to
see who calls the function __len__ with some radically big context but I
can't seem to interpret the output myself (bit too deep in pythons belly
for my level). Code is shown bellow:

import inspect

class Errors:
def __init__(self):
pass
def toFile(self):
pass
def __len__(self):
curframe = inspect.currentframe()
calframe = inspect.getouterframes(curframe, context=15)
for i in range(15):
print " caller: ",calframe[i][3]
print "len is called"
return 0

len(e)

caller: __len__
caller: <module>
caller: runcode
caller: main
caller: <module>
len is called
0

caller: __len__

caller: get_arg_text
caller: fetch_tip
caller: get_the_calltip
caller: localcall
caller: pollresponse
caller: _getresponse
caller: getresponse
caller: handle
caller: __init__
caller: __init__
caller: finish_request
caller: process_request
caller: _handle_request_noblock
caller: handle_request
caller: manage_socket
caller: run
caller: __bootstrap_inner
caller: __bootstrap
len is called
e.toFile(

Maybe that can help? I know it doesn't really, it would be better to print
the class that owns the methods called, however I don't know how to do

len(e)

caller: /home/dino/Desktop/bitbucket/refactor/errors/errors.py
caller: <pyshell#9>
caller: /usr/lib/python2.7/idlelib/run.py
caller: /usr/lib/python2.7/idlelib/run.py
caller: <string>
len is called
0

caller: /home/dino/Desktop/bitbucket/refactor/errors/errors.py

caller: /usr/lib/python2.7/idlelib/CallTips.py
caller: /usr/lib/python2.7/idlelib/CallTips.py
caller: /usr/lib/python2.7/idlelib/run.py
caller: /usr/lib/python2.7/idlelib/rpc.py
caller: /usr/lib/python2.7/idlelib/rpc.py
caller: /usr/lib/python2.7/idlelib/rpc.py
caller: /usr/lib/python2.7/idlelib/rpc.py
caller: /usr/lib/python2.7/idlelib/run.py
caller: /usr/lib/python2.7/SocketServer.py
caller: /usr/lib/python2.7/idlelib/rpc.py
caller: /usr/lib/python2.7/SocketServer.py
caller: /usr/lib/python2.7/SocketServer.py
caller: /usr/lib/python2.7/SocketServer.py
caller: /usr/lib/python2.7/SocketServer.py
caller: /usr/lib/python2.7/idlelib/run.py
caller: /usr/lib/python2.7/threading.py
caller: /usr/lib/python2.7/threading.py
caller: /usr/lib/python2.7/threading.py
len is called
e.toFile(


Thanks for the help,
Dino
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