I was under the impression python string formatting using .format() would correctly use properties, instead I get the default behaviour of an object being string-formatted:
>>> def get(): return "Blah"
>>> a = property(get)
>>> "{a}!".format(a=a)
'<property object at 0x221df18>!'
Is this the intended behaviour, and if so what's a good way to implement a special behaviour for properties (eg, the above test would return "Blah!" instead)?
property objects are descriptors. As such, they don't have any special abilities unless accessed through a class.
something like:
class Foo(object):
@property
def blah(self):
return "Cheddar Cheese!"
a = Foo()
print('{a.blah}'.format(a=a))
should work. (You'll see Cheddar Cheese! printed)
Yes, this is basically the same as if you just did:
>>> def get(): return "Blah"
>>> a = property(get)
>>> print a
If you want "Blah" just call the function:
>>> def get(): return "Blah"
>>> a = property(get)
>>> "{a}!".format(a=a.fget())
Python properties do interop well with .format(). Consider the following example:
>>> class Example(object):
... def __init__(self):
... self._x = 'Blah'
... def getx(self): return self._x
... def setx(self, value): self._x = value
... def delx(self): del self._x
... x = property(getx,setx,delx, "I'm the 'x' property.")
...
>>>
>>> ex = Example()
>>> ex.x
'Blah'
>>> print(ex.x)
'Blah'
>>> "{x.x}!".format(x=ex)
'Blah!'
I believe your problem stems from your property not being part of a class. How are you actually using properties that they aren't working with .format()?
format isn't calling your property. Python is calling your property to resolve the object that it is going to pass to format. That's just a nitpick, but it is a little different than '{x.x}'.format(x=ex) where the property's getter gets called inside the format function/method.