Added dict section

knowledge base/python.md

@@ -1,14 +1,22 @@
 # Python
 
 1. [TL,DR](#tldr)
-2. [Web servers](#web-servers)
+2. [Dictionaries](#dictionaries)
+3. [F-strings](#f-strings)
+4. [Web servers](#web-servers)
    1. [Flask](#flask)
    2. [WSGI server](#wsgi-server)
-3. [Further readings](#further-readings)
+5. [Further readings](#further-readings)
+6. [Sources](#sources)
 
 ## TL,DR
 
 ```py
+# Declare a dictionary.
+{'spam': 2, 'ham': 1, 'eggs': 3}
+dict(spam=2,ham=1,eggs=3)
+dict([('spam',2),('ham',1),('eggs',3)])
+
 # String formatting with f-strings.
 f"Hello, {name}. You are {age}."
 F"{name.lower()} is funny."
@@ -18,6 +26,52 @@ F"{name.lower()} is funny."
 unique_list = list(set(redundant_list))
 ```
 
+## Dictionaries
+
+```py
+# Declare a dictionary.
+d = {'spam': 2, 'ham': 1, 'eggs': 3}
+d = dict(spam=2,ham=1,eggs=3)
+d = dict([('spam',2),('ham',1),('eggs',3)])
+d = {x: x for x in range(5)}
+d = {c.lower(): c + '!' for c in ['SPAM','EGGS','HAM']}
+d = dict.fromkeys('abc',0)
+
+# Change an element.
+d['ham'] = ['grill', 'bake', 'fry']
+
+# Add a new element.
+d['brunch'] = 'bacon'
+
+# Delete an element.
+del d['eggs']
+d.pop('eggs')
+
+# List values and/or keys.
+d.values()
+d.keys()
+d.items()
+
+# Print the elements and their values.
+for k,v in d.items(): print(k,v)
+
+# Merge dictionaries.
+d1 = {'spam': 2, 'ham': 1, 'eggs': 3}
+d2 = {'toast': 4, 'muffin': 5, 'eggs': 7}
+d1.update(d2)
+
+# Copy dictionaries.
+d1 = {'spam': 2, 'ham': 1, 'eggs': 3}
+d2 = d1.copy()
+```
+
+## F-strings
+
+```py
+f"Hello, {name}. You are {age}."
+F"{name.lower()} is funny."
+```
+
 ## Web servers
 
 ### Flask
@@ -25,7 +79,7 @@ unique_list = list(set(redundant_list))
 - `request.args` gets query arguments
 - `request.form` gets POST arguments
 
-```python
+```py
 from flask import request, jsonify
 
 @app.route('/get/questions/', methods=['GET', 'POST','DELETE', 'PATCH'])
@@ -55,7 +109,7 @@ def question():
 
 You can use `waitress`:
 
-```python
+```py
 from flask import Flask
 
 app = Flask(__name__)
@@ -76,6 +130,7 @@ python hello.py
 
 ## Further readings
 
+- [Dictionaries]
 - [PIP]
 - [How To Update All Python Packages]
 - [invl/pip-autoremove]
@@ -90,19 +145,27 @@ python hello.py
 - [An intro to threading in Python]
 - [ThreadPoolExecutor in Python: the complete guide]
 
+## Sources
+
+- [10 python one-liners for dictionaries]
+
+<!-- project's references -->
+[dictionaries]: https://docs.python.org/3/tutorial/datastructures.html#dictionaries
+[logging]: https://docs.python.org/3/howto/logging.html
+
 <!-- internal references -->
 [pip]: ./pip.md
 
 <!-- external references -->
 [*args and **kwargs in python]: https://www.geeksforgeeks.org/args-kwargs-python/
+[10 Python One-Liners for Dictionaries]: https://medium.com/codex/10-python-one-liners-for-dictionaries-d58754386a1d
 [an intro to threading in python]: https://realpython.com/intro-to-python-threading/
 [data types]: https://www.w3schools.com/python/python_datatypes.asp
 [f-strings]: https://realpython.com/python-f-strings/
 [flask at first run: do not use the development server in a production environment]: https://stackoverflow.com/questions/51025893/flask-at-first-run-do-not-use-the-development-server-in-a-production-environmen#54381386
 [flask example with POST]: https://stackoverflow.com/questions/22947905/flask-example-with-post#53725861
+[how to filter list elements in python]: https://www.pythontutorial.net/python-basics/python-filter-list/
 [how to update all python packages]: https://www.activestate.com/resources/quick-reads/how-to-update-all-python-packages/
 [invl/pip-autoremove]: https://github.com/invl/pip-autoremove
-[logging]: https://docs.python.org/3/howto/logging.html
 [multi-value query parameters with flask]: https://dev.to/svencowart/multi-value-query-parameters-with-flask-3a92
 [threadpoolexecutor in python: the complete guide]: https://superfastpython.com/threadpoolexecutor-in-python/
-[how to filter list elements in python]: https://www.pythontutorial.net/python-basics/python-filter-list/