This question already has answers here:
List attributes of an object [duplicate]
(18 answers)
Closed 4 years ago.
For example I have next python class
class Myclass():
a = int
b = int
Imagine that I don't know the name this class, so I need to get the names of attributes? ("a" and "b")
If you want all (including private) attributes, just
dir(Myclass)
Attributes starting with _ are private/internal, though. For example, even your simple Myclass will have a __module__ and an empty __doc__ attribute. To filter these out, use
filter(lambda aname: not aname.startswith('_'), dir(Myclass))
Related
This question already has answers here:
obtaining named attributes of self
(2 answers)
Closed 3 years ago.
I want to know how can I access a class attribute using a string. E.g
class Test:
def __init__(self):
# defined self.name here
self.name.person = 1
If I have the program:
a = "person"
b = Test()
How can I print self.name.person using the variable a?
print(b.name.a)
Many thanks!
Python has getattr() as built-in function:
print(getattr(b.name, a))
This question already has answers here:
How does the #property decorator work in Python?
(15 answers)
How do Python properties work?
(4 answers)
Closed 4 years ago.
I can do
class Foo(object):
x = property(lambda _: 123)
f = Foo()
f.x
to get 123
However, if I try
p = property(lambda : 123)
p
I get
<property object at 0x108f2f3b8>
Now I understand that an member of a class instance is not the same thing as a regular variable but I'm not sure what exactly makes this behavior different.
Does the fact that you instantiate a class somehow do extra binding on property objects? Is it a special case or is it a behavior I can take advantage in other situations and extend? Related - are property objects useful outside of a class declaration? Or is it just for this specific case?
This question already has answers here:
How do I get the string with name of a class?
(5 answers)
Closed 4 years ago.
class A:
pass
> A().__class__.__name__
-->'A'
> A.__class__.__name__
--> 'type'
How can I get 'A' without the parens?
You're getting 'type', because the class of a class definition is... type (in other words: a class definition is a type).
You can just use the __name__ attribute. No need to look for the __class__, you already have the class:
A.__name__
'A'
Just to make it completely clear:
A().__class__ is A
True
This question already has answers here:
Class (static) variables and methods
(27 answers)
What is the difference between class and instance attributes?
(5 answers)
Closed 5 years ago.
If I define a simple class
class someClass():
var = 1
x = someClass()
someClass.var = 2
This will make x.var equal 2. This is confusing to be because normally
something akin to this like:
a = 1
b = a
a = 2
will leave b intact as b==1. So why is this not the same with class variables? Where is the difference? Can call all class variables mutable?
In a way the class variables work more like assigning a list to a=[1] and doing a[0]=2.
Basically the problem is how is x.var acessing someClass.var it must be something different then is used when two variables are set equal in python. What is happening?
var is a static class variable of someClass.
When you reach out to get x.var, y.var or some_other_instance.var, you are accessing the same variable, not an instance derived one (as long as you didn't specifically assigned it to the instance as a property).
This question already has answers here:
Why can't you add attributes to object in python? [duplicate]
(2 answers)
Can't set attributes on instance of "object" class
(7 answers)
Closed 9 years ago.
I just realized that:
class A(object): pass
a = A()
a.x = 'whatever'
Works (does not raise an error and creates a new x member).
But this:
a = object()
a.x = 'whatever'
Raises:
AttributeError: 'object' object has no attribute 'x'
While I probably would never use this in real production code, I'm a bit curious about what the reason is for the different behaviors.
Any hints ?
Probably because of __slots__. By default your class have dict of all atributes which can be added to like in your first example. But that behaviour can bi overriden by using slots.
Also, some classes like datetime which are implemented in C also can not be extended with new attributes at runtime.
Workaround for such classes is to do something like :
class MyObject(): # extend that class, here we extend object
pass # add nothing to the class
o = MyObject()
o.x = 'whatever' # works