is it a bug ?

[Sylvain Ferriol]

hello
can you explain to me what happened:

class toto(object):
eq = float.__eq__

t = toto()

getattr(t,'eq')
TypeError: descriptor '__eq__' for 'float' objects doesn't apply to
'toto' object

[Peter Otten]

Sylvain Ferriol wrote:

can you explain to me what happened:

class toto(object):
eq = float.__eq__

t = toto()

getattr(t,'eq')
TypeError: descriptor '__eq__' for 'float' objects doesn't apply to
'toto' object

float.__eq__ is probably implemented in C and its operation will make sense
only for instances of float or subclasses of float. Try

>>class Toto(float):

.... eq = float.__eq__
....

>>Toto().eq(42)

False

Peter

[Fredrik Lundh]

Sylvain Ferriol wrote:

can you explain to me what happened:

class toto(object):
eq = float.__eq__

t = toto()

getattr(t,'eq')
TypeError: descriptor '__eq__' for 'float' objects doesn't apply to
'toto' object

I'd say the error message explains it pretty well. what did you expect
this to do?

</F>

[Sylvain Ferriol]

Fredrik Lundh a écrit :

Sylvain Ferriol wrote:

>can you explain to me what happened:

class toto(object):
eq = float.__eq__

t = toto()

getattr(t,'eq')
TypeError: descriptor '__eq__' for 'float' objects doesn't apply to
'toto' object

I'd say the error message explains it pretty well. what did you expect
this to do?

i just want a class variable named 'eq', i could understand if its name
was '__eq__'.
class toto(object):
__eq__ = float.__eq__

why i can not create some class variables like this ?
class toto(object):
a= float.__eq__
b= str.__eq__
......

</F>

[Sylvain Ferriol]

Peter Otten a écrit :

Sylvain Ferriol wrote:

>>can you explain to me what happened:

class toto(object):
eq = float.__eq__

t = toto()

getattr(t,'eq')
TypeError: descriptor '__eq__' for 'float' objects doesn't apply to
'toto' object

float.__eq__ is probably implemented in C and its operation will make sense
only for instances of float or subclasses of float. Try

>>>>class Toto(float):

.... eq = float.__eq__
....

>>>>Toto().eq(42)

False

i can not use it because:
class toto(float):
def __init__(self,a=None):pass

t=toto(a=3)
TypeError: 'a' is an invalid keyword argument for this function

Peter

[Fredrik Lundh]

Sylvain Ferriol wrote:

i just want a class variable named 'eq'

so why are you assigning another class' descriptor to it? descriptors
are bound to types, and only works properly if used with the type they
were created for.

why i can not create some class variables like this ?

class toto(object):
a= float.__eq__
b= str.__eq__

but given that "toto" is neither a float nor a str, what do you expect
that code to *do*?

is this some "programming by random mutation" exercise?

</F>

[Peter Otten]

Sylvain Ferriol wrote:

>>>>>class Toto(float):

....*****eq*=*float.__eq__
....

>>>>>Toto().eq(42)

False

i can not use it because:
class toto(float):
def*__init__(self,a=None):pass

t=toto(a=3)
TypeError: 'a' is an invalid keyword argument for this function

Override __new__() then:

>>class Toto(float):

.... def __new__(cls, a=None):
.... if a is None:
.... a = 42
.... return float.__new__(cls, a)
.... def __init__(cls, a=None):
.... print "random message containing", a
....

>>Toto()

random message containing None
42.0

>>Toto(42)

random message containing 42
42.0

Peter