Challenge 1: Write a GET/POST Function-Based View — Possible Solution
====================================================================

# catalog/views.py

from django.http import HttpResponse

def subscribe(request):
    if request.method == "POST":
        email = request.POST.get("email", "")
        if not email:
            return HttpResponse("Please provide an email address.", status=400)
        return HttpResponse(f"Thanks — {email} is now subscribed!")

    # request.method == "GET"
    form_html = """
        <form method="post">
            <input type="email" name="email" placeholder="you@example.com">
            <button type="submit">Subscribe</button>
        </form>
    """
    return HttpResponse(form_html)

# catalog/urls.py
from django.urls import path
from . import views

urlpatterns = [
    path("subscribe/", views.subscribe, name="subscribe"),
]

WHY THIS WORKS
--------------
- Branching on request.method inside a single function is the standard
  FBV pattern for "one URL, two behaviors depending on HTTP verb" — the
  same route (/subscribe/) shows a form on GET and processes it on POST.
- request.POST.get("email", "") reads the form field by its `name`
  attribute — using .get() with a default avoids a KeyError if the field
  is somehow missing from the submitted data.
- Every branch has an explicit `return HttpResponse(...)` — including the
  early-return validation check for a missing email — which is exactly
  the discipline the chapter's gotcha calls out: Django will raise a real
  error if any code path falls through without returning a proper
  response object.