Add structural subtyping

Signed-off-by: Jakub Walczak <jakub.walczak@p.lodz.pl>

Author: jamesWalczak

_toc.yml

@@ -8,14 +8,14 @@ parts:
     - file: context_managers
     - file: iterators
     - file: generators
+    - file: generics
     - file: structural_subtyping
     - file: higher_order_functions
     - file: decorators
     - file: metaclasses
     - file: descriptors
     - file: code_inspect
     - file: dynamic_execution
-    - file: generics
     - file: weakref
     - file: coroutines_and_concurrency
     - file: parallelism

generics.md

@@ -16,4 +16,11 @@ kernelspec:
 ````{admonition} This chapter is not ready yet?
 :class: important
 Writing a book takes time and for that chapter I did not have enough of it. Please, return later.
-````
+````
+
+
+## Variance types
+Let us explain slightly here the type of type variance we have in Python what was explained in PEP483 {cite}`pep-0483`. In general, types can be:
+1. covariant,
+2. contravariant,
+3. invariant

intro.md

@@ -158,6 +158,12 @@ Iterating over sources of data
 Generating content and `yield` keyword
 :::
 
+:::{grid-item-card} [Generic collections](generics.md) 📦
+:class-header: bg-light
+
+Type-safe collection handling
+:::
+
 :::{grid-item-card} [Structural subtyping](structural_subtyping.md) 👣
 :class-header: bg-light
 
@@ -200,12 +206,6 @@ Stack tracing, callable signature management, and more
 And its pros and cons
 :::
 
-:::{grid-item-card} [Generic collections](generics.md) 📦
-:class-header: bg-light
-
-Type-safe collection handling
-:::
-
 :::{grid-item-card} [Weak references](weakref.md) 🔗
 :class-header: bg-light
 

references.bib

@@ -234,4 +234,28 @@ @techreport{pep-0479
   month       = {November},
   url         = {https://peps.python.org/pep-0479/},
   urldate     = {2025-10-21}
+}
+
+@techreport{pep-0544,
+  author      = {Levkivskyi, Ivan and  Lehtosalo, Jukka and Langa, Łukasz},
+  title       = {{PEP} 544 -- Protocols: Structural subtyping (static duck typing)},
+  institution = {Python Software Foundation},
+  type        = {Python Enhancement Proposal},
+  number      = {544},
+  year        = {2017},
+  month       = {March},
+  url         = {https://peps.python.org/pep-0544/},
+  urldate     = {2025-10-23}
+}
+
+@techreport{pep-0483,
+  author      = {van Rossum, Guido and Levkivskyi, Ivan},
+  title       = {{PEP} 483 -- The Theory of Type Hints},
+  institution = {Python Software Foundation},
+  type        = {Python Enhancement Proposal},
+  number      = {483},
+  year        = {2014},
+  month       = {December},
+  url         = {https://peps.python.org/pep-0483/},
+  urldate     = {2025-10-23}
 }

special_attributes.md

@@ -292,6 +292,10 @@ There are two main exceptions:
 
 ## Of Classes
 
+### Attributes
+
+#### `__mro__`
+
 ## Of Objects
 
 ### Attributes