cURL & HTTP Terms in Python

Learn how to use cURL effectively and gain a deep understanding of core HTTP terminology, concepts, and components used in real-world Python backend systems.

What is cURL

cURL is a command-line tool that allows you to send HTTP requests directly from your terminal. As a Python backend developer (especially when working with FastAPI), cURL is one of the most important tools for testing APIs without building a frontend.

1. Definition of cURL

What cURL actually is.

2. Why Backend Developers Use cURL

Practical backend usage.

Using cURL

Below examples assume you have a Python FastAPI server running on port 8000. For example, your server might be running at: http://localhost:8000

1. GET Requests

Fetching data.

2. POST Requests

Sending request body.

3. Debugging with cURL

Inspecting raw HTTP.

Form Data with cURL

APIs do not always receive JSON. Traditional HTML forms send data differently. Here are two common formats:

1. Sending Form Data

Using application/x-www-form-urlencoded and multipart/form-data.

HTTP Overview

HTTP (HyperText Transfer Protocol) defines how clients and servers communicate. All modern Python APIs use HTTP.

1. Request–Response Model

How HTTP communication works.

2. Stateless Nature of HTTP

Why HTTP does not remember clients.

HTTP Methods

HTTP methods describe the intention of a request.

1. Read & Safe Methods

Methods that do not modify data.

2. Write & Modify Methods

Methods that change server state.

HTTP Headers

Headers provide additional information about the request or response.

1. Request Headers

Headers sent by clients.

2. Response Headers

Headers sent by servers.

Status Code & Status Message

Every HTTP response contains a status code and a status message.

1. Status Code

Numeric response indicator.

2. Status Message

Human-readable description.

HTTP Body

The HTTP body contains the actual data being transmitted.

1. Request Body

Data sent by client.

2. Response Body

Data returned by server.

Cookies & State

Although HTTP is stateless, cookies help maintain user sessions.

1. What Are Cookies

Client-side storage.

2. Cookies vs Headers

Where cookies fit in HTTP.