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Wert App is a PyQt5 desktop application built around a clear separation of concerns across four layers: a presentation layer that owns all visual widgets and stylesheets, a logic layer that handles user-facing workflows, a data layer that manages a MySQL database, and an integration layer that wraps two external HTTP APIs. Each layer communicates only with the layers directly adjacent to it, keeping the codebase easy to extend without touching unrelated code.

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Layer breakdown

The application is divided into four distinct layers, each with a well-defined responsibility. 1. Presentation layer — Assets/windows/ and Assets/styles/ All PyQt5 UI layouts live under Assets/windows/. Three UI files define the visual skeleton of each window:
  • widget_login.py (uiLogin) — login form layout
  • widget_register.py (uiRegister) — registration form layout
  • main_window.py (uiWert) — the full main window with notes, currency converter, and economic-data panels
Assets/styles/stylesheet.py wraps each raw UI class with a styled base class (loginStyle, registerStyle, mainWindowStyle). These base classes apply Qt stylesheets (colors, fonts, border radii) and configure alignment and echo modes so the logic layer inherits a fully-styled widget tree without embedding style details in business logic. 2. Logic layer — modules/ Each module contains a single class that subclasses the corresponding style base class and wires up all signal/slot connections:
  • logica_login.py (ventanaLogin) — validates credentials via DatabaseManager, then opens ventanaMain or ventanaRegister
  • logica_register.py (ventanaRegister) — validates new-user input (non-empty fields, password length ≥ 6, password match) then calls DatabaseManager.setRegister
  • logica_main_window.py (ventanaMain) — orchestrates notes CRUD, currency conversion via ChangeAPi, and economic-data lookups via WorldBankAPI
3. Data layer — database/
  • conexion.py — reads the database password from passwordBDD.txt, provides getConexion() to open a mysql.connector connection, and provides setTables() to create the usuarios and notas tables if they do not already exist
  • db_operations.py — DatabaseManager receives an open connection in its constructor and exposes eight methods covering user registration, login, note creation, retrieval, and deletion
4. Integration layer — api/
  • world_bank_api.py — WorldBankAPI queries the World Bank REST API for country lists, economic indicators, and historical data series
  • change_api.py — ChangeAPi queries the ExchangeRate-API v6 for live currency conversion rates

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Application startup flow

main.py is the single entry point. It performs three steps before the event loop starts:
1

Ensure database tables exist

setTables() is called first. It opens its own connection, runs CREATE TABLE IF NOT EXISTS for usuarios, and then runs CREATE TABLE for notas (skipping silently if the table already exists).
2

Create the QApplication instance

QApplication(sys.argv) initialises the Qt runtime. No window is shown yet.
3

Show the login window

A ventanaLogin instance is created and shown. ventanaLogin.__init__ opens a persistent MySQL connection and creates a DatabaseManager bound to that connection, which is then shared with any child windows.
import sys
from modules.logica_login import ventanaLogin
from PyQt5.QtWidgets import QApplication
from database.db_operations import DatabaseManager
from database.conexion import setTables, getConexion

def main():
    if __name__ == '__main__':
        setTables()
        app = QApplication(sys.argv)
        ventana_log = ventanaLogin()
        ventana_log.show()
        sys.exit(app.exec_())

main()

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Window flow

Once the event loop is running, windows open and close in a linear sequence driven by user actions.
1

ventanaLogin (entry point)

The login window is always shown first. The user can either submit credentials or click the register button.
  • Register button → ventanaRegister opens as a secondary window while the login window stays visible.
  • Successful login → ventanaLogin closes itself and opens ventanaMain, passing the shared DatabaseManager instance and the authenticated username.
2

ventanaRegister (optional)

Opens on top of the login window. On successful registration it closes itself; the login window remains so the user can sign in immediately.
3

ventanaMain (authenticated session)

The main application window. It holds all three feature panels — notes, currency converter, and economic data — in a single QMainWindow. It owns references to both API client objects (WorldBankAPI and ChangeAPi) and uses the DatabaseManager passed from the login window for all note operations.

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Explore further

Database design and operations

MySQL schema, table definitions, and the full DatabaseManager API reference.

External API integrations

How WorldBankAPI and ChangeAPi wrap external HTTP services and handle errors.

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