CODEWITHSUNDEEP
pythonpython-2.7
Tal
Tal

Reputation: 1215

Why is not a class?

I write this class:

class Sensor:
    def __init__ (self,sensor_class_name, data):
        self.sensor_class_name = sensor_class_name
        self.data              = data

When I do this check:

if type(Sensor) == type:
    print("type")

else:
    print("not type")

It returns not type.

When I do this check on built in class, it returns type.

Why Sensor is not a class?

Upvotes: 1

Views: 189

Answers (6)

Tal
Tal

Reputation: 1215

I just inherit the class from object, and now it say it a class.

class Sensor (object):
    def __init__ (self,sensor_class_name, data):
        self.sensor_class_name = sensor_class_name
        self.data              = data

Upvotes: 0

dbr
dbr

Reputation: 169543

In ancient versions of Python (before v2.2) a class was a special thing (classobj), separate from a type:

>>> class OldStyleClass:
...     pass
...
>>> type(OldStyleClass)
<type 'classobj'>

This is an "old style class"

Python 2.2 onwards you should generally always use "new style" classes, which are defined by inheriting from object (or some subclass of it):

>>> class NewStyleClass(object):
...     pass
...
>>> type(NewStyleClass)
<type 'type'>

There is a good post about the history of classes in Python, explaining the distinction - "New-style Classes" on The History of Python blog (written by the creator of Python)

In Python 3, this distinction was removed, so both of the class definitions above would be identical:

>>> class Blah:
...     pass
...
>>> type(Blah)
<class 'type'>
>>>
>>> class Blah(object):
...     pass
...
>>> type(Blah)
<class 'type'>

Upvotes: 0

Vishnu Upadhyay
Vishnu Upadhyay

Reputation: 5061

In new style classes so that inherite from object class every class object is instance of type class.

print isinstance(Sensor, type) # True

    class Sensor:
        def __init__ (self,sensor_class_name, data):
            ..
            ..
    if type(Sensor) == type:
        print("type")  
    else:
        print("not type")
    print isinstance(Sensor, type)

Ouput:-
    >>> 
    not type
    Flase

While in newstyle classes :-

class Sensor(object):
     ...
     ...
print isinstance(Sensor, type)
>>> 
type
True

also:-

In [52]: class A: pass

In [53]: type(A)
Out[53]: classobj

In [54]: class B(object):pass

In [55]: type(B)
Out[55]: type

In [56]: B.__class__
Out[56]: type

In [57]: A.__class__
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-57-5b54bd730948> in <module>()
----> 1 A.__class__

AttributeError: class A has no attribute '__class__'

Upvotes: 0

Javier Castellanos
Javier Castellanos

Reputation: 9874

Because types derive from objects:

In python2 classes without a parent class are type classobj. In python3 this changed and classes without parent class the inherit by default from object.

class A: pass
print type(A)
<type 'classobj'>


class B(object): pass
print type(B)
<type 'type'>

check this link for more info:https://wiki.python.org/moin/NewClassVsClassicClass

Upvotes: 0

Maroun
Maroun

Reputation: 95958

You are creating a class of the old (pre 2.2) Python using a plain class statement.

>>> type(Sensor)
<type 'classobj'>

Try:

>>> import types
>>> types.ClassType is type(Sensor)
True

A class statement without bases creates a classic class. In order to create a new style class you have to specify object as the base.

types.ClassType resembles <type 'type'>, instances of it are types.

Upvotes: 3

Tanveer Alam
Tanveer Alam

Reputation: 5275

>>> import types
>>> dir(types)
['BooleanType', 'BufferType', 'BuiltinFunctionType', 'BuiltinMethodType', 'ClassType', 'CodeType', 'ComplexType', 'DictProxyType', 'DictType', 'DictionaryType', 'EllipsisType', 'FileType', 'FloatType', 'FrameType', 'FunctionType', 'GeneratorType', 'GetSetDescriptorType', 'InstanceType', 'IntType', 'LambdaType', 'ListType', 'LongType', 'MemberDescriptorType', 'MethodType', 'ModuleType', 'NoneType', 'NotImplementedType', 'ObjectType', 'SliceType', 'StringType', 'StringTypes', 'TracebackType', 'TupleType', 'TypeType', 'UnboundMethodType', 'UnicodeType', 'XRangeType', '__builtins__', '__doc__', '__file__', '__name__', '__package__']

>>> class Sensor:
...     pass
... 
>>> if type(Sensor) == types.ClassType:
...     print "type"
... else:
...     print "not type"
... 
type
>>> type(type)
<type 'type'>
>>> type(Sensor)
<type 'classobj'>

type itself is type of types module.

Class is type of ClassType.

Upvotes: 0

Related Questions