chapter 2.1 calculator project setup

calculator/pkg/calculator.py

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+# calculator.py
+
+class Calculator:
+    def __init__(self):
+        self.operators = {
+            "+": lambda a, b: a + b,
+            "-": lambda a, b: a - b,
+            "*": lambda a, b: a * b,
+            "/": lambda a, b: a / b,
+        }
+        self.precedence = {
+            "+": 1,
+            "-": 1,
+            "*": 2,
+            "/": 2,
+        }
+
+    def evaluate(self, expression):
+        if not expression or expression.isspace():
+            return None
+        tokens = expression.strip().split()
+        return self._evaluate_infix(tokens)
+
+    def _evaluate_infix(self, tokens):
+        values = []
+        operators = []
+
+        for token in tokens:
+            if token in self.operators:
+                while (
+                    operators
+                    and operators[-1] in self.operators
+                    and self.precedence[operators[-1]] >= self.precedence[token]
+                ):
+                    self._apply_operator(operators, values)
+                operators.append(token)
+            else:
+                try:
+                    values.append(float(token))
+                except ValueError:
+                    raise ValueError(f"invalid token: {token}")
+
+        while operators:
+            self._apply_operator(operators, values)
+
+        if len(values) != 1:
+            raise ValueError("invalid expression")
+
+        return values[0]
+
+    def _apply_operator(self, operators, values):
+        if not operators:
+            return
+
+        operator = operators.pop()
+        if len(values) < 2:
+            raise ValueError(f"not enough operands for operator {operator}")
+
+        b = values.pop()
+        a = values.pop()
+        values.append(self.operators[operator](a, b))

calculator/pkg/render.py

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+# render.py
+
+def render(expression, result):
+    if isinstance(result, float) and result.is_integer():
+        result_str = str(int(result))
+    else:
+        result_str = str(result)
+
+    box_width = max(len(expression), len(result_str)) + 4
+
+    box = []
+    box.append("┌" + "─" * box_width + "┐")
+    box.append(
+        "│" + " " * 2 + expression + " " * (box_width - len(expression) - 2) + "│"
+    )
+    box.append("│" + " " * box_width + "│")
+    box.append("│" + " " * 2 + "=" + " " * (box_width - 3) + "│")
+    box.append("│" + " " * box_width + "│")
+    box.append(
+        "│" + " " * 2 + result_str + " " * (box_width - len(result_str) - 2) + "│"
+    )
+    box.append("└" + "─" * box_width + "┘")
+    return "\n".join(box)