mirror of
https://github.com/satwikkansal/wtfpython.git
synced 2024-09-11 20:17:08 +03:00
New example: The chicken-egg problem
Closes https://github.com/satwikkansal/wtfpython/issues/101
This commit is contained in:
parent
9b3b367b45
commit
f365271df3
48
README.md
vendored
48
README.md
vendored
@ -731,6 +731,54 @@ Even when the values of `x` were different in every iteration prior to appending
|
|||||||
|
|
||||||
---
|
---
|
||||||
|
|
||||||
|
### ▶ The chicken-egg problem ^
|
||||||
|
|
||||||
|
1\.
|
||||||
|
```py
|
||||||
|
>>> isinstance(3, int)
|
||||||
|
True
|
||||||
|
>>> isinstance(type, object)
|
||||||
|
True
|
||||||
|
>>> isinstance(object, type)
|
||||||
|
True
|
||||||
|
```
|
||||||
|
|
||||||
|
2\. So which is the ultimate, base class? And wait, there's more to the confusion
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> class A: pass
|
||||||
|
>>> isinstance(A, A)
|
||||||
|
False
|
||||||
|
>>> isinstance(type, type)
|
||||||
|
True
|
||||||
|
>>> isinstance(object, object)
|
||||||
|
True
|
||||||
|
```
|
||||||
|
|
||||||
|
3\.
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> issubclass(int, object)
|
||||||
|
True
|
||||||
|
>>> issubclass(type, object)
|
||||||
|
True
|
||||||
|
>>> issubclass(object, type)
|
||||||
|
False
|
||||||
|
```
|
||||||
|
|
||||||
|
|
||||||
|
#### 💡 Explanation
|
||||||
|
|
||||||
|
- `type` is a [metaclass](https://realpython.com/python-metaclasses/) in Python.
|
||||||
|
- **Everything** is an `object` in Python, which includes classes as well as their objects (instances).
|
||||||
|
- class `type` is the metaclass of class `object`, and every class (including `type`) has inherited directly or indirectly from `object`.
|
||||||
|
- There is no real base class among `object` and `type`. The confusion in the above snippets is arising because we're thinking these relationships (`issubclass` and `isinstance`) in terms of Python classes. The relationship between `object` and `type` can't be reproduced in pure python. To be more precise the following relationships can't be reproduced in pure Python,
|
||||||
|
+ class A is instance of class B, and class B is an instance of class A.
|
||||||
|
+ class A is an instance of itself.
|
||||||
|
- These relationships between `object` and `type` (both being instances of eachother as well as themselves) exist in Python because of "cheating" at implementation level.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
### ▶ `is not ...` is not `is (not ...)`
|
### ▶ `is not ...` is not `is (not ...)`
|
||||||
|
|
||||||
```py
|
```py
|
||||||
|
Loading…
Reference in New Issue
Block a user