Now I have to design a class that overload __getattr__, but after
that, I found the __repr__ have been affected. This is a simple
example model:
#!/usr/bin/env python
class test:
def __init__(self):
self.x = 1
def __getattr__(sel f, attr_name):
try:
return self.__dict__[attr_name]
except KeyError:
self.__dict__[attr_name] = 'inexistent'
return self.__dict__[attr_name]
t = test()
print t.x
print t.y
print type(t)
T = t
print T.x
print t
So far, I want the operation "print t" still return "<test instance
at ...>", but the reuslt is:
sh$ python test.py
1
inexistent
<type 'instance'>
1
Traceback (most recent call last):
File "testtree.p y", line 23, in ?
print t
TypeError: 'str' object is not callable
I also tried to overload __repr__ itself:
#!/usr/bin/env python
class test:
def __init__(self):
self.x = 1
def __getattr__(sel f, attr_name):
try:
return self.__dict__[attr_name]
except KeyError:
self.__dict__[attr_name] = 'inexistent'
return self.__dict__[attr_name]
def __repr__(self):
return 'test.__repr__'
t = test()
print t.x
print t.y
print type(t)
T = t
print T.x
print t
But the result remains:
Traceback (most recent call last):
File "testtree.p y", line 23, in ?
print t
TypeError: 'str' object is not callable
So why? What is the principles?
7  2334 
En Fri, 22 Jun 2007 00:30:43 -0300, Roc Zhou <ch*******@gmai l.com>
escribió:
Now I have to design a class that overload __getattr__, but after
that, I found the __repr__ have been affected. This is a simple
example model:
You are creating many attributes with value "inexistent ", even special
methods. Put a print statement and see what happens:
#!/usr/bin/env python
class test:
def __init__(self):
self.x = 1
def __getattr__(sel f, attr_name):
try:
return self.__dict__[attr_name]
except KeyError:
print "Now creating:",attr _name
self.__dict__[attr_name] = 'inexistent'
return self.__dict__[attr_name]
--
Gabriel Genellina
I know what's wrong. Thank you. And I think
try:
return self.__dict__[attr_name]
is unnecessary, because python will do it itself for us.
So now I have to overload __str__, but how can I make self.__str__
print as builtin str(): at here, I want get the result like:
<test instance at 0xb7bbb90c>
?
On 6 22 , 12 55 , "Gabriel Genellina" <gagsl-...@yahoo.com.a r>
wrote:
En Fri, 22 Jun 2007 00:30:43 -0300, Roc Zhou <chowro...@gmai l.com>
escribió:
Now I have to design a class that overload __getattr__, but after
that, I found the __repr__ have been affected. This is a simple
example model:
You are creating many attributes with value "inexistent ", even special
methods. Put a print statement and see what happens:
#!/usr/bin/env python
class test:
def __init__(self):
self.x = 1
def __getattr__(sel f, attr_name):
try:
return self.__dict__[attr_name]
except KeyError:
print "Now creating:",attr _name
self.__dict__[attr_name] = 'inexistent'
return self.__dict__[attr_name]
--
Gabriel Genellina
return hex(id(self))
On 6 22 , 1 48 , Roc Zhou <chowro...@gmai l.comwrote:
I know what's wrong. Thank you. And I think
try:
return self.__dict__[attr_name]
is unnecessary, because python will do it itself for us.
So now I have to overload __str__, but how can I make self.__str__
print as builtin str(): at here, I want get the result like:
<test instance at 0xb7bbb90c>
?
On 6 22 , 12 55 , "Gabriel Genellina" <gagsl-...@yahoo.com.a r>
wrote:
En Fri, 22 Jun 2007 00:30:43 -0300, Roc Zhou <chowro...@gmai l.com>
escribió:
Now I have to design a class that overload __getattr__, but after
that, I found the __repr__ have been affected. This is a simple
example model:
You are creating many attributes with value "inexistent ", even special
methods. Put a print statement and see what happens:
#!/usr/bin/env python
class test:
def __init__(self):
self.x = 1
def __getattr__(sel f, attr_name):
try:
return self.__dict__[attr_name]
except KeyError:
print "Now creating:",attr _name
self.__dict__[attr_name] = 'inexistent'
return self.__dict__[attr_name]
--
Gabriel Genellina
I'm sorry but I still have a question, look at this example:
>>class test:
.... def __init__(self):
.... self.x = 1
.... def __getattr__(sel f, attr_name):
.... print attr_name
.... if attr_name == 'y':
.... return 2
.... else:
.... raise AttributeError, attr_name
....
>>t = test()
t.x
1
>>t.y
y
2
>>print t.x
1
>>print t
__str__
__repr__
<__main__.tes t instance at 0xb7f6d6cc>
Since __str__ and __repr__ does not exist because their names was
printed, why not the "AttributeError " be raised?
En Fri, 22 Jun 2007 02:48:50 -0300, Roc Zhou <ch*******@gmai l.com>
escribió:
I know what's wrong. Thank you. And I think
try:
return self.__dict__[attr_name]
is unnecessary, because python will do it itself for us.
Exactly; by the time __getattr__ is called, you already know attr_name is
not there.
So now I have to overload __str__, but how can I make self.__str__
print as builtin str(): at here, I want get the result like:
<test instance at 0xb7bbb90c>
?
I would do the opposite: *only* create inexistent attributes when they are
not "special". This way you don't mess with Python internals.
.... def __getattr__(sel f, name):
.... if name[:2]!='__' or name[-2:]!='__':
.... self.__dict__[name] = 'inexistent'
.... return self.__dict__[name]
.... raise AttributeError, name
This way you don't create "fake" attributes for things like __bases__ by
example, and dir(), vars(), repr() etc. work as expected.
--
Gabriel Genellina
En Fri, 22 Jun 2007 03:43:26 -0300, Roc Zhou <ch*******@gmai l.com>
escribió:
I'm sorry but I still have a question, look at this example:
>>>class test:
... def __init__(self):
... self.x = 1
... def __getattr__(sel f, attr_name):
... print attr_name
... if attr_name == 'y':
... return 2
... else:
... raise AttributeError, attr_name
...
>>>t = test()
t.x
1
>>>t.y
y
2
>>>print t.x
1
>>>print t
__str__
__repr__
<__main__.tes t instance at 0xb7f6d6cc>
Since __str__ and __repr__ does not exist because their names was
printed, why not the "AttributeError " be raised?
This is the implementation of str() in action; tries to find a __str__
method and fails; tries to find a __repr__ instead and fails; then uses
the default representation.
See <http://docs.python.org/ref/customization.h tml#l2h-179>
--
Gabriel Genellina
Roc Zhou wrote:
I'm sorry but I still have a question, look at this example:
>>>class test:
... def __init__(self):
... self.x = 1
... def __getattr__(sel f, attr_name):
... print attr_name
... if attr_name == 'y':
... return 2
... else:
... raise AttributeError, attr_name
...
>>>t = test()
t.x
1
>>>t.y
y
2
>>>print t.x
1
>>>print t
__str__
__repr__
<__main__.tes t instance at 0xb7f6d6cc>
Since __str__ and __repr__ does not exist because their names was
printed, why not the "AttributeError " be raised?
Because classic classes invoke
t.__getattr__(s elf, "__repr__")
and expect that to return a proper __repr__() method -- unless __getattr__()
raises an AttributeError:
>>class Test:
.... def __getattr__(sel f, name):
.... if name == "__repr__":
.... raise AttributeError
.... return "<inexisten t %r>" % name
....
>>t = Test()
t
<__main__.Tes t instance at 0x401d42ac>
If you use newstyle classes you won't run into that particular problem:
>>class Test(object):
.... def __getattr__(sel f, name):
.... return "<inexisten t %r>" % name
....
>>t = Test()
t
<__main__.Tes t object at 0x401d426c>
>>t.yadda
"<inexisten t 'yadda'>" This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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example model:
#!/usr/bin/env python
class test:
def __init__(self):
self.x = 1
def __getattr__(self, attr_name):
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example model:
#!/usr/bin/env python
class test:
def __init__(self):
self.x = 1
def __getattr__(self, attr_name):
try:
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