Why does ' dir(1) is dir(True) ' return False

Question

From this quieston's answer

is will return True if two variables point to the same object, == if the objects referred to by the variables are equal.

Aren't dir(1) and dir(True) point to the same object? Both of them prints a list of the same methods. Am I missing something about object here?

>>> dir(1) == dir(True)
True
>>> dir(1) is dir(True)
False
>>>

They point to two distinct objects, which happen to have the same content — Valentin Lorentz, May 22 '16 at 12:57

Antti Haapala -- Слава Україні · Accepted Answer · 2016-05-22T14:14:54.837

First of all, True is not 1:

>>> True is not 1
True

Second, as the documentation says

dir([object])

[...] With an argument, attempt to return a list of valid attributes for that object.

If the object has a method named __dir__(), this method will be called and must return the list of attributes. This allows objects that implement a custom __getattr__() or __getattribute__() function to customize the way dir() reports their attributes.

If the object does not provide __dir__(), the function tries its best to gather information from the object’s __dict__ attribute, if defined, and from its type object. The resulting list is not necessarily complete, and may be inaccurate when the object has a custom __getattr__().

The resulting list is sorted alphabetically. [...]

Now, int and bool both have the __dir__ slot filled from object.__dir__:

>>> int.__dir__
<method '__dir__' of 'object' objects>
>>> bool.__dir__
<method '__dir__' of 'object' objects>

And the documentation for object.__dir__ adds this one extra bit of information:

object.__dir__(self)

Called when dir() is called on the object. A sequence must be returned. dir() converts the returned sequence to a list and sorts it.

As the documentation says, dir constructs a new list for each invocation and then sorts it. (We could also look into the code for _dir_object which calls PySequence_List on the return value of __dir__; PySequence_List takes a sequence as an argument, and returns a new list with the same elements as the original sequence; this newly created list is then sorted and returned)

>>> a = 1
>>> dir(a) is dir(a)
False

Third, True is an instance of type bool, which is a subclass of int.

 >>> isinstance(True, bool)
 True
 >>> isinstance(1, int)
 True
 >>> issubclass(bool, int)
 True
 >>> isinstance(True, int)
 True

Additionally, bool does not add any methods that are not already present in int. And because the resulting list is sorted alphabetically,

>>> dir(1) == dir(True)
True

@StefanPochmann the documentation says that `dir()` gathers the data from the object's `__dict__` attribute, and then sorts it alphabetically. However I need to add a clarification that there is `__dir__` there — Antti Haapala -- Слава Україні, May 22 '16 at 13:15
If `(1).__dir__()` always returns the same list and the "conversion" is like `if not isinstance(x, list): x = list(x)` and the sorting is like `x.sort()`, then `dir` would always return the same list, not a new one. — Stefan Pochmann, May 22 '16 at 13:38
Ha, I don't really like reading the C code, I'll just trust what you say there. That's the source code, though, not the documentation. — Stefan Pochmann, May 22 '16 at 15:36

score 2 · Answer 2 · answered May 22 '16 at 12:59

2

Everytime thet you execute dir the new object is created.

>>> dir(True) is dir(True)
False

answered May 22 '16 at 12:59

mucka

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score 0 · Answer 3 · answered May 22 '16 at 13:08

0

dir creates a new object for the int that it's returning each time.

Basically you got confused between 1 is True and dir(1) is dir(True) and dir(1) == dir(True).

answered May 22 '16 at 13:08

Amit Gold

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Why does ' dir(1) is dir(True) ' return False

3 Answers3