Tutorial 5 — Input Validation

Tutorial 5: Validación de Inputs

This tutorial demonstrates PyGo’s native validator package — struct-based validation with built-in and custom rules.

🎯 What You’ll Learn

• Define validation rules using struct tags
• Use built-in validators (required, email, uuid, min, max)
• Create custom validation rules
• Integrate validation into HTMX forms

📝 Step 1: Define Validatable Model

from validator import ValidateStruct

model UserSignup:
  email: Email        # Built-in email validation
  name: String        # Built-in string type
  password: String    # Validated via rules below
  age: Integer?       # Optional, validated if present
  country: String     # Required

# Add validation rules inline
def validate(self) -> List[String]:
  errors = []

  # Email is already Email type (built-in validation)
  if not self.email:
    errors.append("Email is required")

  # Password rules
  if len(self.password) < 8:
    errors.append("Password must be at least 8 characters")

  if len(self.password) > 128:
    errors.append("Password too long")

  # Age validation (optional field)
  if self.age is not None:
    if self.age < 13:
      errors.append("Must be at least 13 years old")
    if self.age > 120:
      errors.append("Invalid age")

  # Country must be 2-letter code
  if len(self.country) != 2:
    errors.append("Country must be 2-letter country code")

  return errors

📝 Step 2: Use in Handler with HTMX

handler signup:
  signup(user_data: Dict) -> String:
    # Parse into model
    user = UserSignup(
      email=user_data["email"],
      name=user_data["name"],
      password=user_data["password"],
      age=int(user_data.get("age", 0)) or None,
      country=user_data["country"],
    )

    # Validate
    errors = user.validate()

    if errors:
      # HTMX swaps this partial into the form
      return """
      <div class="alert alert-error">
        <ul>
        {% for error in errors %}
          <li>{{ error }}</li>
        {% endfor %}
        </ul>
      </div>
      """

    # Success — create user
    user.save()
    return redirect("/welcome")

📝 Step 3: HTML Form with Error Display

<form
  hx-post="/signup"
  hx-swap="outerHTML"
  hx-on::afterRequest="if(htmx.channeled) htmx.trigger(this, 'reset')"
>
  <div>
    <label>Email</label>
    <input type="email" name="email" required />
  </div>

  <div>
    <label>Name</label>
    <input type="text" name="name" required />
  </div>

  <div>
    <label>Password</label>
    <input type="password" name="password" required minlength="8" />
  </div>

  <div>
    <label>Age (optional)</label>
    <input type="number" name="age" min="13" max="120" />
  </div>

  <div>
    <label>Country (2-letter code)</label>
    <input type="text" name="country" maxlength="2" required />
  </div>

  <button type="submit">Sign Up</button>
</form>

<!-- Errors are injected here by HTMX response -->
<div id="form-errors"></div>

📋 Built-in Validation Rules

Type	Validation	Description
Email	format	RFC 5322 email validation
UUID	format	UUID v4 format
String	length	min/max bounds
Integer	range	min/max bounds
Boolean	type	true/false
DateTime?	nullable	Optional datetime

🔧 Custom Validation Rules

from validator import AddRule

# Register a custom rule
AddRule("strong_password", lambda p: len(p) >= 8 and any(c.isupper() for c in p) and any(c.isdigit() for c in p))

model UserSignup:
  password: String
  # validator checks password against "strong_password" rule automatically

🧪 Testing Validation

# Test validation in Python context
def test_user_validation():
  user = UserSignup(
    email="invalid-email",
    password="weak",
    country="USA",
  )

  errors = user.validate()
  assert len(errors) == 3  # invalid email, weak password, invalid country

🚀 Next Steps

• Tutorial 6: Email with Mailer
• Validator API Reference
• pygo-i18n — for localized validation messages