Forem: Pri

Understanding Lambda Functions in Python: Definition, Usage, and Applications

Pri — Tue, 19 Aug 2025 02:02:32 +0000

What is a `lambda` Function?

In simple terms, a lambda function is a small anonymous function, meaning it is defined without a name. A lambda function can take any amount of arguments; however, it is only able to have one expression.

lambda functions are typically used inside of other functions like map(), filter(), or sort(). It does not need to be assigned to a variable, so it behaves like a function that is defined with def. It is important to keep in mind that it does not replace def, as lambda functions are limited to a single expression.`

How Do We Use `lambda` Functions?

Syntax:

Key Points:

lambda is the keyword used to define the function.
It can take any number of arguments.
No return statement needed because it evaluates and returns the value of the expression automatically.
Usually used for simple functions.
It is like a "throwaway" function. If writing a complete function is unnecessary and you only need it temporarily, try using a lambda function!

Example:

If you were to square a number using a regular function, you would write something like this:

The lambda function equivalent is this:

How Are `lambda` Functions Useful?

lambda functions show their practicality when used inside of another function.

If you have a function definition taking in one argument and that argument is multiplied by a number that is unknown, it would look something like this:

You are now able to use this function definition to create a function that always doubles... or triples the number you input:

Using a `lambda` Function With `filter()`, `map()`, and `sort()`

`filter()` - used to filter specific values from a set of data.

filter(function, iterable) only keeps the elements for which the function returns True. The lambda x: x % 2 == 0 checks if the numbers are even, one-by-one. filter() applies the lambda to every element of numbers (the list of integers [1-10]) and keeps only the ones that return True (the even ones). filter() returns an iterator, so we wrap it in list() to see the filtered results.

`map()` - applies a function to every element.

map(function, iterable) applies the function to every element of the numbers list. The lambda x: x * 2 doubles each number on that list.

`sort()` With `key` - sorting logic that is custom.

The sort(key=function) decides how to order the elements by using the function's return value. The lambda x: len(x) sorts each fruit by length rather than by alphabetical order.

`lambda` Function Use Cases

In the real world, you may use lambda with something like filtering an email from a list, so if you were looking for only @gmail.com addresses, you would be able to keep the @gmail.com addresses.

You may use lambda when mapping through a list to calculate item prices with tax. That way, lambda would multiply each price to add a tax.

Lastly, you could use a lambda function to sort through people by age, that way your return is the age of each person and sort() would organize it from youngest to oldest.

How will you try using a `lambda` function?

References

BroCode. (2024, July 14). Learn Python LAMBDA in 6 minutes! 🚮. YouTube. https://www.youtube.com/watch?v=IljPHDyBRog

How are lambdas useful?. Stack Overflow. (2009, May 20). https://stackoverflow.com/questions/890128/how-are-lambdas-useful

Kumar, R. (2022, September 4). Powerful use-cases of lambda function in Python💪. Medium. https://medium.com/@ravikumar10593/powerful-use-cases-of-lambda-function-in-python-d4ccefe5f3d2

Reshef, G. (2021, December 8). What is the purpose of lambda expressions?. Discuss Python. https://discuss.python.org/t/what-is-the-purpose-of-lambda-expressions/12415

W3schools.com. W3Schools Online Web Tutorials. (n.d.). https://www.w3schools.com/python/python_lambda.asp

Understanding the React useContext Hook and How to Use It

Pri — Wed, 23 Jul 2025 01:39:04 +0000

Prior to the release of the useContext hook in React 16.8 on February 6th, 2019, developers relied on prop drilling, render props, and third-party libraries. While functional, these approaches led to several issues, such as reduced readability and maintainability (prop drilling), more complex and less intuitive components (render props), and added complexity with boilerplate code (third-party libraries). The useContext hook offers an efficient and seamless option to share state between components.

What is the `useContext` hook?

The useContext hook provides a simpler way to pass data through the component tree without manually passing props at every level. In a typical React application, data is passed from a parent component to a child via props. This can be inefficient when certain values are required by multiple components across the application. The useContext hook simplifies this process, eliminating the need to explicitly pass props through every level of the tree.

Why use `useContext` instead of props?

Since useContext is designed to share data, it can be considered "global" for a component tree—much like a theme, preferred language, or authenticated user. By using the useContext hook, you avoid passing props through intermediate components. If your data needs to be accessible by many components at various nesting levels and you want to avoid prop drilling, useContext is the ideal solution.

Example showing props being passed through nested components:

How do you use the `useContext` hook?

Create context: Import createContext and initialize it.

import { useState, createContext } from "react";
import ReactDOM from "react-dom/client";

const UserContext = createContext()

Context Provider: Wrap the components that need access to the context with a UserContext.Provider. All child components within this tree will have access to the context.

function ComponentOne() {
  const [user, setUser] = useState("John Doe");

  return (
    <UserContext.Provider value={user}>
      <h1>{`Hello ${user}!`}</h1>
      <ComponentTwo user={user} />
    </UserContext.Provider>
  );
}

Using the useContext hook: Include useContext in the import statement for the component where you need the data. As long as you do this, you will be able to access the data in any component. Make sure to include a function declaration and a variable name.

import { useState, createContext, useContext } from "react";

function ComponentFive() {
  const user = useContext(UserContext);

  return (
    <>
      <h1>Component Five</h1>
      <h2>{`Hello ${user} again!`}</h2>
    </>
  );
}

Complete Example Using the useContext Hook

import { useState, createContext, useContext } from "react";  // import createContext
import ReactDOM from "react-dom/client";

const UserContext = createContext();  // initialize createContext

function ComponentOne() {
  const [user, setUser] = useState("John Doe");

  return (  // wrap the child components in Context Provider and include the state value
    <UserContext.Provider value={user}> 
      <h1>{`Hello ${user}!`}</h1>
      <ComponentTwo />
    </UserContext.Provider>
  );
}

// all components will have access to the user context
// to use useContext in a child component, we need to access it using the useContext Hook
function ComponentTwo() {
  return (
    <>
      <h1>Component Two</h1>
      <ComponentThree />
    </>
  );
}

function ComponentThree() {
  return (
    <>
      <h1>Component Three</h1>
      <ComponentFour />
    </>
  );
}

function ComponentFour() {
  return (
    <>
      <h1>Component Four</h1>
      <ComponentFive />
    </>
  );
}

//  include the useContext hook in the import statement for the component you want the data in
import { useState, createContext, useContext } from "react";

function ComponentFive() { //  you can access the user context in all components where you import the data
  const user = useContext(UserContext);

  return (
    <>
      <h1>Component Five</h1>
      <h2>{`Hello ${user} again!`}</h2>
    </>
  );
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<ComponentOne />);

References

Context. React. (n.d.). https://legacy.reactjs.org/docs/context.html#:~:text=Passing%20Data%20Deeply%20with%20Context,every%20level%20of%20the%20tree.
Pedro. (2020, October 2). UseContext Hook Tutorial In ReactJS | Global States. YouTube. https://www.youtube.com/watch?v=lnL6gRkQ5g8
React useContext Hook. W3Schools Online Web Tutorials. (n.d.). https://www.w3schools.com/react/react_usecontext.asp
ReactJS useContext Hook. GeeksforGeeks. (2025, March 5). https://www.geeksforgeeks.org/reactjs/reactjs-usecontext-hook/

A Straightforward Guide to Building and Using a JSON Database File

Pri — Tue, 31 Dec 2024 00:43:07 +0000

What is a `db.json` file?

A db.json file is a JavaScript Object Notation (JSON) file that is used to store and transport organized data in a format that is easy to read; often when data is sent from a server to a web page.

JSON is language independent, meaning the JSON syntax is developed from JavaScript object notation syntax, but the JSON format is only in text format. The code used for reading and creating JSON data can be written in other programming languages.

Why is a `db.json` file ideal?

A db.json file is lightweight, easy to read, and does not require a complex setup, which makes it easy for developers to understand and modify data. db.json files are ideal for local development or prototyping frontend applications. During development, data often needs to be stored somewhere temporarily without needing to set up a full database; a db.json file provides that simple solution.

Certain tools, such as a JSON Server can transform a db.json file into a completely functional mock REST API. A mock REST API server "imitates a real API server by providing realistic responses to requests" (API Mocking Guide and Online Mock API Server Testing). This allows frontend developers to test API calls without a backend and mock-up a model of an application with realistic API responses.

For example, a db.json file like this:

{
  "topFiveUniversities": [
    {"id": 1, "name": "University of Oxford"},
    {"id": 2, "name": "Massachusetts Institute of Technology"},
    {"id": 3, "name": "Harvard University"},
    {"id": 4, "name": "Princeton University"},
    {"id": 5, "name": "University of Cambridge"}
 ]
}

Can get a result in API endpoints like:
GET /topFiveUniversities: Retrieves the full list of universities
POST /topFiveUniversities: Adds a new university
PUT /topFiveUniversities/1: Updates the university with id:1
DELETE /topFiveUniversities/1: Deletes the university with id:1

What is the structure of a `db.json` file?

The following syntax defines dog breeds object, which are an array of three dog breed records (objects):

{
"dogBreeds":[
  {"breed": "Bernese Mountain Dog", "origin":"Switzerland"},
  {"breed": "Dogo Argentino", "origin":"Argentina"},
  {"breed": "Chihuahua", "origin":"Mexico"}
]
}

The top-level key is "dogBreeds" (an array). The array items are each item in the array, which are objects with two key-value pairs "breed" and "origin."

Be sure to use camelCase or snake_case and avoid spaces in keys (e.g., "dog breeds"), as it can cause difficulties when constructing URLs and potential issues when accessing the keys in your code.

Rules of JSON Syntax

The data is organized as name/value pairs
The commas separate elements in arrays or key-value pairs in objects (except the last one)
The curly braces hold the objects
The square brackets hold the arrays

Breakdown of JSON Data

Name and Value

Name or value pairs are used in JSON data writing, much like the properties of JavaScript. A name or value pair has a field name in double quotation marks (" "), followed by a colon (:), followed by a value in double quotes (" "):

"breed":"Bernese Mountain Dog"

JSON names must have double quotes; JavaScript does not.

Objects

The objects in a JSON file are written in curly braces. They can contain more than one name or value pairs, like in JavaScript:

{"breed":"Bernese Mountain Dog", "origin":"Switzerland"}

Each name/value pairs should be separated by a comma and space.

Arrays

The arrays in a JSON file are written in square brackets. An array can contain objects, like in JavaScript:

"dogBreeds":[
  {"breed": "Bernese Mountain Dog", "origin":"Switzerland"},
  {"breed": "Dogo Argentino", "origin":"Argentina"},
  {"breed": "Chihuahua", "origin":"Mexico"}
]

As seen above, the object "dogBreeds" is an array which contains three objects. Each object is stored information of a specific breed and its origin.

Some things to Keep in mind when building a `db.json file

If you open a curly brace {} or square bracket [], make sure to close them.
Include commas between array or objects
Use double quotes (" ") for strings
Do not include comments (JSON does not allow them)

Transforming JSON Text into a JavaScript Object

It is useful to convert a JSON text to a JavaScript object in cases where you may need to work with structured data in a more interactive manner. JSON is commonly used to read data from a web server and display it on a web page. You can use a string as input to structure it in a simple way. You can do this by creating a JavaScript string that contains JSON syntax:

You can use the JavaScript built-in function JSON.parse() to change the string into a JavaScript object:

Lastly, in your page, use the new JavaScript object:

Using a `db.json` file with a project

Node.js and npm will need to be installed on your computer. Continue onto the following steps to set up and use JSON Server in your application:

1. Install the JSON Server

In your terminal or command prompt, navigate to your project directory and type:

npm install -g json-server

This will globally install the JSON Server in your computer.

2. Create a JSON File

In your project directory, create a JSON file using VSCode or a code editor of your choice. Your JSON file should have a .json file extension, such as db.json. This is where you will write your JSON data.

3. Construct Your Data

Establish your data inside the db.json file as an array of objects or an object with nested objects. Each object should have a unique id, as it represents a data entity.

4. Start the JSON Server

Start your JSON Server by typing the following into your terminal:

json-server --watch db.json

This will run by default on http://localhost:3000. Access the API at http://localhost:3000.

References

“API Mocking Guide and Online Mock API Server Testing.” Stoplight - A Smartbear Company, https://stoplight.io/mock-api-guide#:~:text=A%20mock%20API%20server%20imitates,types%2C%20objects%2C%20and%20arrays. Accessed Dec. 2024.

“JavaScript JSON.” W3Schools Online Web Tutorials, www.w3schools.com/js/js_json.asp. Accessed Dec. 2024.

Ofoegbu, Juliet. “How to Use JSON Server for Front-End Development.” freeCodeCamp.Org, freeCodeCamp.org, 21 Aug. 2023, www.freecodecamp.org/news/json-server-for-frontend-development/.

What Is JSON | Explained, Hostinger Academy, 24 Nov. 2022, https://youtu.be/cj3h3Fb10QY?feature=shared. Accessed July 2024.

“World University Rankings.” Times Higher Education (THE), 16 Dec. 2024, www.timeshighereducation.com/world-university-rankings/latest/world-ranking.

Forem: Pri

Understanding Lambda Functions in Python: Definition, Usage, and Applications

What is a lambda Function?

How Do We Use lambda Functions?

Syntax:

Key Points:

Example:

How Are lambda Functions Useful?

Using a lambda Function With filter(), map(), and sort()

filter() - used to filter specific values from a set of data.

map() - applies a function to every element.

sort() With key - sorting logic that is custom.

lambda Function Use Cases

How will you try using a lambda function?

References

Understanding the React useContext Hook and How to Use It

What is the useContext hook?

Why use useContext instead of props?

How do you use the useContext hook?

Complete Example Using the useContext Hook

References

A Straightforward Guide to Building and Using a JSON Database File

What is a db.json file?

Why is a db.json file ideal?

What is the structure of a db.json file?

Rules of JSON Syntax

Breakdown of JSON Data

Name and Value

Objects

Arrays

Some things to Keep in mind when building a `db.json file

Transforming JSON Text into a JavaScript Object

Using a db.json file with a project

References

What is a `lambda` Function?

How Do We Use `lambda` Functions?

How Are `lambda` Functions Useful?

Using a `lambda` Function With `filter()`, `map()`, and `sort()`

`filter()` - used to filter specific values from a set of data.

`map()` - applies a function to every element.

`sort()` With `key` - sorting logic that is custom.

`lambda` Function Use Cases

How will you try using a `lambda` function?

What is the `useContext` hook?

Why use `useContext` instead of props?

How do you use the `useContext` hook?

What is a `db.json` file?

Why is a `db.json` file ideal?

What is the structure of a `db.json` file?

Using a `db.json` file with a project