[New Concept Docs]: Anonymous Functions (lambdas) in Python

[BethanyG]

This issue describes how to implement the anonymous functions (lambdas) in Python concept docs.
You can find the related concept exercise issue here
There was some previous discussion in the old concept exercise issue, which you can find here.

If you have not yet contributed to concept documents, this issue will require some upfront reading to give you the needed background knowledge.

✅ Getting started

Please please read the docs before starting. Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time.

General Contributing Docs:

• Contributing to Exercism | Exercism and GitHub | - Contributor Pull Request Guide
• What are those Weird Task Tags about?
• Exercism Formatting and Style Guide
• Exercism Markdown Specification
• Reputation

Documents on Language Tracks and Concepts:

• Building Language Tracks: An Overview
• What are Concepts?
• Concept Specifications

🎯 Goal

These concept docs are meant to teach an understanding/use/creation of anonymous functions (lambdas) in Python.

💡 Learning objectives

• Understand what an anonymous function is, and how to create one
  • The syntax of creating a lambda
  • Using different function argument flavors with lambda
• Understand the differences between lambdas and Pythons "regular" functions
• Understand what problems are solved by using a lambda
• The pitfalls of lambdas, and when to avoid them
• Using lambdas as key functions in other situations such as sort() , sorted(), min(), and max()
• Applying arguments to a lambda via IIFE (immediately invoked function expression)
• Anti-patterns when using lambdas

🚫 Out of scope

Concepts and Subjects that are Out of Scope (click to open)

• comprehensions
• lambdas in comprehensions
• comprehensions in lambdas
• using a decorator on a lambda
• functools (this will get its own exercise)
• generators
• map(), filter(), and reduce() (these will get their own exercise)
• using an assignment expression or "walrus" operator (:=) in a lambda
• assigning a variable to a lambda
• using a lambda where a named function is recommended/better

🤔 Concepts

Concepts and Related Concepts this Concept Covers (click to open)

• anonymous-functions
• lambdas
• functions,
• higher-order functions
• functions as arguments
• functions as returns
• nested funcitons

↩️ Prerequisites

These are the concepts/concept exercises the student should be familiar with before taking on/learning this concept.

Prereqs (click to open)

• basics
• booleans
• comparisons
• dicts
• dict-methods
• functions
• function-arguments
• higher-order functions
• iteration
• lists
• list-methods
• numbers
• sequences
• sets
• strings
• string-methods
• tuples

📚 Resources to refer to

Resources (click to open)

• Python Docs: Defining Functions
• Python Docs Tutorial: Lambda Expressions
• Functions as Objects in Python
• Composing Programs: Higher-Order Functions
• Learn by Example: Python Lambda Function
• Real Python: How to Use Python Lambda Fuctions
• Trey Hunner: Overusing Lambda expressions in Python

📁 Files to Be Created

File Detail for these Concept Docs (click to collapse/em>)

Please see the following for more details on these files: concepts links.json For more information, see concept links file The same resources listed in this issue can be used as a starting point for the concepts/links.json file, if it doesn't already exist. If there are particularly good/interesting information sources for this concept that extend or supplement the concept exercise material & the resources already listed -- please add them to the links.json document. Concept about.md For more information, see Concept about.md This file provides information about this concept for a student who has completed the corresponding concept exercise. It is intended as a reference for continued learning. Concept introduction.md For more information, see Concept introduction.md This can also be a summary/paraphrase of the about.md document listed above, and will provide a brief introduction of the concept for a student who has not yet completed the associated concept or practice exercises. It should contain a good summation of the concept, but not go into lots of detail. Concept .meta/config.json Entries For more information, see Concept .meta/config.json This file is likely already stubbed out. Remember to add a concept blurb of less than 350 characters. Please also add your GitHub username to the "authors" array, and any contributor GitHub usernames to the "contributors" array.

🎶 Implementation Notes

• Example code should only use syntax & concepts introduced within these docs or one of the prerequisite concept exercises or documents. Where possible, please use REPL formatting, unless you are demonstrating pseudo code or a long code block.
  Please do not use syntax not previously covered in prerequisite topics or exercises. Please also follow PEP8 guidelines.
• Our markdown and JSON files are checked against prettier . We recommend setting prettier up locally and running it prior to submitting your PR to avoid any CI errors.

🆘 Next Steps & Getting Help

1. If you'd like to work on this issue, comment saying "I'd like to work on this" (there is no real need to wait for a response, just go ahead, we'll assign you and put a [claimed] label on the issue).
2. If you have any questions while implementing, please post the questions as comments in here, or contact one of the maintainers on our Slack channel.