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New example: The chicken-egg problem
Closes https://github.com/satwikkansal/wtfpython/issues/101
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README.md
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README.md
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@ -730,6 +730,54 @@ Even when the values of `x` were different in every iteration prior to appending
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---
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### ▶ The chicken-egg problem ^
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1\.
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```py
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>>> isinstance(3, int)
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True
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>>> isinstance(type, object)
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True
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>>> isinstance(object, type)
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True
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```
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2\. So which is the ultimate, base class? And wait, there's more to the confusion
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```py
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>>> class A: pass
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>>> isinstance(A, A)
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False
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>>> isinstance(type, type)
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True
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>>> isinstance(object, object)
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True
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```
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3\.
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```py
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>>> issubclass(int, object)
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True
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>>> issubclass(type, object)
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True
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>>> issubclass(object, type)
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False
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```
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#### 💡 Explanation
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- `type` is a [metaclass](https://realpython.com/python-metaclasses/) in Python.
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- **Everything** is an `object` in Python, which includes classes as well as their objects (instances).
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- class `type` is the metaclass of class `object`, and every class (including `type`) has inherited directly or indirectly from `object`.
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- 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,
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+ class A is instance of class B, and class B is an instance of class A.
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+ class A is an instance of itself.
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- These relationships between `object` and `type` (both being instances of eachother as well as themselves) exist in Python because of "cheating" at implementation level.
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---
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### ▶ `is not ...` is not `is (not ...)`
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```py
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