Do we really need @staticmethod decorator in python to declare static method

You need the decorator if you intend to try to call the @staticmethod from the instance of the class instead of of the class directly

class Foo():
    def bar(x):
        return x + 5

>>> f = Foo()
>>> f.bar(4)
Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    f.bar(4)
TypeError: bar() takes 1 positional argument but 2 were given

Now if I declare @staticmethod the self argument isn't passed implicitly as the first argument

class Foo():
    @staticmethod
    def bar(x):
        return x + 5

>>> f = Foo()
>>> f.bar(4)
9

The documentation describes some transformations that are done when calling a user defined method:

Note that the transformation from function object to (unbound or bound) method object happens each time the attribute is retrieved from the class or instance. In some cases, a fruitful optimization is to assign the attribute to a local variable and call that local variable. Also notice that this transformation only happens for user-defined functions; other callable objects (and all non-callable objects) are retrieved without transformation. It is also important to note that user-defined functions which are attributes of a class instance are not converted to bound methods; this only happens when the function is an attribute of the class.

For methods marked as staticmethod this is different:

Static method objects provide a way of defeating the transformation of function objects to method objects described above. A static method object is a wrapper around any other object, usually a user-defined method object. When a static method object is retrieved from a class or a class instance, the object actually returned is the wrapped object, which is not subject to any further transformation. Static method objects are not themselves callable, although the objects they wrap usually are. Static method objects are created by the built-in staticmethod() constructor.