New example: The chicken-egg problem

satwikkansal · satwikkansal · commit 9ea7ab0c5a05 · 2019-06-09T00:07:02.000+05:30
Closes satwikkansal#101
diff --git a/README.md b/README.md
@@ -730,6 +730,54 @@ 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 ...)`
 
 ```py
