fastapi: added put doc

Docs/Services/FastAPI/05-Put-Method.md

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+# FastAPI – PUT Method 
+
+This document demonstrates how to use the **HTTP PUT method** in FastAPI to update an existing resource.
+It builds on previous GET and POST examples and completes a basic CRUD-style workflow.
+
+---
+
+## Example Application
+
+Create or update `main.py` with the following content:
+
+```python
+from fastapi import FastAPI
+
+app = FastAPI()
+
+users = [
+    {"name": "abbas", "age": 20},
+    {"name": "mmd", "age": 37},
+    {"name": "asghar", "age": 19},
+]
+
+
+@app.get("/")
+def home_page():
+    return {"msg": "API is working"}
+
+
+@app.get("/users")
+def show_users():
+    return users
+
+
+@app.post("/create_user")
+def create_user(name: str, age: int):
+    new_user = {"name": name, "age": age}
+    users.append(new_user)
+    return {"msg": f"user {name} with age {age} created"}
+
+
+@app.put("/update_user/{target_name}")
+def update_user(target_name: str, age: int):
+    for user in users:
+        if user["name"] == target_name:
+            user["age"] = age
+            return {"msg": f"user {target_name} updated"}
+    return {"msg": "user not found"}
+```
+
+---
+
+## Code Overview
+
+### PUT Endpoint Definition
+
+```python
+@app.put("/update_user/{target_name}")
+def update_user(target_name: str, age: int):
+```
+
+* Registers an HTTP **PUT** endpoint
+* `target_name` is a **path parameter**
+* `age` is a **query parameter**
+* Used to update an existing user’s data
+
+---
+
+### Update Logic
+
+```python
+for user in users:
+    if user["name"] == target_name:
+        user["age"] = age
+```
+
+* Iterates over the in-memory users list
+* Matches user by name
+* Updates the `age` field in place
+
+---
+
+### Success Response
+
+```json
+{
+  "msg": "user abbas updated"
+}
+```
+
+Returned when the target user exists and is updated successfully.
+
+---
+
+### Failure Response
+
+```json
+{
+  "msg": "user not found"
+}
+```
+
+Returned when no matching user exists.
+
+---
+
+## Example Requests
+
+### Update User Age (PUT)
+
+```bash
+curl -X PUT "http://localhost:8000/update_user/abbas?age=25"
+```
+
+### Verify Update
+
+```http
+GET /users
+```
+
+Updated response:
+
+```json
+[
+  {"name": "abbas", "age": 25},
+  {"name": "mmd", "age": 37},
+  {"name": "asghar", "age": 19}
+]
+```
+
+---
+
+## Running the Application
+
+Start the service using `uvicorn`:
+
+```bash
+uvicorn main:app --reload
+```
+
+---
+
+## HTTP Method Summary
+
+| Method | Endpoint              | Purpose                 |
+| ------ | --------------------- | ----------------------- |
+| GET    | `/`                   | Health check            |
+| GET    | `/users`              | Retrieve all users      |
+| POST   | `/create_user`        | Create a new user       |
+| PUT    | `/update_user/{name}` | Update an existing user |
+
+---
+
+## Best Practices
+
+* Use **PUT** for full updates and **PATCH** for partial updates
+* Return proper HTTP status codes (`404`, `200`, `201`)
+* Avoid using in-memory data stores in production
+* Use Pydantic models for request bodies instead of query parameters
+* Add input validation and error handling
+* Separate routes, services, and models as the project grows
+* Make PUT operations idempotent
+