# Simple GUI Calculator with PyQt5

This guide demonstrates how to create a desktop calculator application using **PyQt5**. PyQt is a set of Python bindings for the Qt application framework, allowing you to build cross-platform GUI applications.

**Modules Used:**
*   `PyQt5`: The Python binding for the Qt framework.

## Installation

```bash
pip install PyQt5
```

## The Code

Save this as `calculator.py`.

```python
import sys
from PyQt5.QtWidgets import QApplication, QWidget, QVBoxLayout, QGridLayout, QPushButton, QLineEdit
from PyQt5.QtCore import Qt

class Calculator(QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("PyQt5 Calculator")
        self.setGeometry(100, 100, 300, 400)
        self.init_ui()

    def init_ui(self):
        # Main Layout
        main_layout = QVBoxLayout()
        self.setLayout(main_layout)

        # Display Screen
        self.display = QLineEdit()
        self.display.setAlignment(Qt.AlignRight)
        self.display.setReadOnly(True)
        self.display.setFixedHeight(50)
        # Increase font size
        font = self.display.font()
        font.setPointSize(20)
        self.display.setFont(font)
        
        main_layout.addWidget(self.display)

        # Buttons Layout
        grid_layout = QGridLayout()
        main_layout.addLayout(grid_layout)

        buttons = [
            ('7', 0, 0), ('8', 0, 1), ('9', 0, 2), ('/', 0, 3),
            ('4', 1, 0), ('5', 1, 1), ('6', 1, 2), ('*', 1, 3),
            ('1', 2, 0), ('2', 2, 1), ('3', 2, 2), ('-', 2, 3),
            ('0', 3, 0), ('.', 3, 1), ('=', 3, 2), ('+', 3, 3),
            ('C', 4, 0)
        ]

        for btn_text, row, col in buttons:
            button = QPushButton(btn_text)
            button.setFixedHeight(60)
            # Connect button click to handler
            button.clicked.connect(lambda checked, text=btn_text: self.on_button_click(text))
            
            # Special styling for operators
            if btn_text in ['/', '*', '-', '+', '=']:
                button.setStyleSheet("background-color: #f0ad4e; color: white; font-size: 18px;")
            elif btn_text == 'C':
                button.setStyleSheet("background-color: #d9534f; color: white; font-size: 18px;")
            else:
                button.setStyleSheet("font-size: 18px;")

            # Add to grid
            # If it's the Clear button, make it span multiple columns for aesthetics
            if btn_text == 'C':
                grid_layout.addWidget(button, row, col, 1, 4)
            else:
                grid_layout.addWidget(button, row, col)

    def on_button_click(self, text):
        if text == '=':
            try:
                # Evaluate the expression
                # Note: eval() can be dangerous if input is not controlled, 
                # but in a calculator with fixed buttons, it's generally acceptable for simple use.
                expression = self.display.text()
                result = str(eval(expression))
                self.display.setText(result)
            except Exception:
                self.display.setText("Error")
        elif text == 'C':
            self.display.clear()
        else:
            current_text = self.display.text()
            
            # Prevent multiple decimals
            if text == '.' and '.' in current_text.split()[-1]:
                 return

            # Handle error state reset
            if current_text == "Error":
                current_text = ""
                
            self.display.setText(current_text + text)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    calc = Calculator()
    calc.show()
    sys.exit(app.exec_())
```

## Usage

1.  Run the script:
    ```bash
    python calculator.py
    ```
2.  A window will appear with a functional calculator interface.

[[programming/python/python]]