Added Tkinter calculator

src/anu-calculator/calculator.py

@@ -0,0 +1,98 @@
+import tkinter as tk
+from tkinter import messagebox
+import ast
+import operator as op
+
+class Calculator(tk.Tk):
+    def __init__(self):
+        super().__init__()
+        self.title("Simple Calculator")
+        self.geometry("420x500")
+        self.resizable(False, False)
+
+        self.create_widgets()
+
+    # --- Safe expression evaluator (no eval()) ---
+
+    def safe_eval(self, expr):
+        allowed_ops = {
+            ast.Add: op.add,
+            ast.Sub: op.sub,
+            ast.Mult: op.mul,
+            ast.Div: op.truediv,
+            ast.Pow: op.pow
+        }
+
+        def _eval(node):
+            if isinstance(node, ast.Num):  # number
+                return node.n
+            elif isinstance(node, ast.BinOp) and type(node.op) in allowed_ops:
+                return allowed_ops[type(node.op)](_eval(node.left), _eval(node.right))
+            else:
+                raise ValueError("Invalid Expression")
+
+        try:
+            parsed = ast.parse(expr, mode='eval').body
+            return _eval(parsed)
+        except Exception:
+            raise ValueError("Invalid Expression")
+
+    # --- GUI setup ---
+    def create_widgets(self):
+        self.entry = tk.Entry(self, font=("Arial", 20), borderwidth=5, relief="sunken", justify='right')
+        self.entry.grid(row=0, column=0, columnspan=4, pady=10, padx=10, ipady=10)
+
+        buttons = [
+            ('7', 1, 0), ('8', 1, 1), ('9', 1, 2), ('/', 1, 3),
+            ('4', 2, 0), ('5', 2, 1), ('6', 2, 2), ('*', 2, 3),
+            ('1', 3, 0), ('2', 3, 1), ('3', 3, 2), ('-', 3, 3),
+            ('0', 4, 0), ('.', 4, 1), ('+', 4, 2), ('=', 4, 3),
+        ]
+
+        for (text, row, col) in buttons:
+            if text == '=':
+                btn = tk.Button(self, text=text, width=5, height=2, font=("Arial", 18),
+                                bg="#4CAF50", fg="white", command=self.calculate)
+            else:
+                btn = tk.Button(self, text=text, width=5, height=2, font=("Arial", 18),
+                                command=lambda t=text: self.append_char(t))
+            btn.grid(row=row, column=col, padx=5, pady=5)
+
+        tk.Button(self, text='C', width=5, height=2, font=("Arial", 18),
+                  bg="#f44336", fg="white", command=self.clear).grid(row=5, column=0, padx=5, pady=5)
+
+        tk.Button(self, text='⌫', width=5, height=2, font=("Arial", 18),
+                  bg="#ff9800", fg="white", command=self.backspace).grid(row=5, column=1, padx=5, pady=5)
+
+        tk.Button(self, text='Exit', width=11, height=2, font=("Arial", 18),
+                  bg="#607d8b", fg="white", command=self.quit).grid(row=5, column=2, columnspan=2, padx=5, pady=5)
+
+        # Keyboard bindings
+        self.bind('<Return>', lambda e: self.calculate())
+        self.bind('<BackSpace>', lambda e: self.backspace())
+        for key in "0123456789+-*/.":
+            self.bind(key, lambda e, k=key: self.append_char(k))
+
+    # --- Button functions ---
+    def append_char(self, char):
+        self.entry.insert(tk.END, char)
+
+    def clear(self):
+        self.entry.delete(0, tk.END)
+
+    def backspace(self):
+        current = self.entry.get()
+        self.entry.delete(0, tk.END)
+        self.entry.insert(0, current[:-1])
+
+    def calculate(self):
+        try:
+            expression = self.entry.get()
+            result = self.safe_eval(expression)
+            self.entry.delete(0, tk.END)
+            self.entry.insert(tk.END, str(result))
+        except Exception:
+            messagebox.showerror("Error", "Invalid Expression")
+
+if __name__ == "__main__":
+    Calculator().mainloop()