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Properties accessed twice for classes defined interactively #102

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ipython opened this Issue May 10, 2010 · 2 comments

2 participants

IPython: interactive computing in Python Fernando Perez
IPython: interactive computing in Python
Owner
ipython commented May 10, 2010

Original Launchpad bug 297501: https://bugs.launchpad.net/ipython/+bug/297501
Reported by: fdo.perez (Fernando Perez).

Reported on the ipython-user list:

I am experiencing some unusual behavior only when I am directly
working in the ipython shell. The problem involves the get method for
a property.

class MyClass():
   def __init__(self):
       self._x = 3
   def getx(self):
       print "getting x"
       return self._x
   def setx(x):
       print "setting x"
       self._x = x
   x = property(getx, setx)

a = MyClass()
a.x           # prints "getting x" twice
print a.x  # prints "getting x" once

If you stick all this in a file and do 'run test.py', the problem does
not occur. Also, notice that it does not occur in the "print a.x"
statement.

IPython: interactive computing in Python
Owner
ipython commented May 10, 2010

[ LP comment 1 by: Fernando Perez, on 2008-11-13 06:47:47.661256+00:00 ]

This is indeed happening, and it's another manifestation of the problems with getattr that have also been reported here:

https://bugs.launchpad.net/ipython/+bug/244677

Similarly, the problem can be avoided by turning %autocall completely off. We still need to investigate whether we can fine-tune %autocall to still work while producing less spurious getattr calls.

Fernando Perez
Owner

Honestly, I don't think this is fixable while having autocall active. Autocall needs to inspect the objects fairly aggressively and I don't think we can make it work without triggering getattrs. The answer is simply: if your objects have so many side effects that you can't call getattr on them more than once, disable autocall altogether.

Closing here.

Fernando Perez fperez closed this November 27, 2011
Damián Avila damianavila referenced this issue from a commit July 30, 2013
Commit has since been removed from the repository and is no longer available.
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