add mymath.py with multiply and divide functions

mymath.py

@@ -0,0 +1,34 @@
+def multiply(a, b):
+    """返回两个数字的乘积"""
+    return a * b
+
+
+def divide(a, b):
+    """返回两个数字的商，b不能为零"""
+    if b == 0:
+        raise ValueError("除数不能为零")
+    return a / b
+
+
+if __name__ == "__main__":
+    # 测试乘法
+    assert multiply(3, 4) == 12
+    assert multiply(-2, 5) == -10
+    assert multiply(0, 100) == 0
+    print("乘法测试通过")
+
+    # 测试除法
+    assert divide(10, 2) == 5
+    assert divide(9, 3) == 3
+    assert divide(5, 2) == 2.5
+    print("除法测试通过")
+
+    # 测试除零异常
+    try:
+        divide(1, 0)
+        print("ERROR: 除零异常未触发")
+    except ValueError as e:
+        assert str(e) == "除数不能为零"
+        print("除零异常测试通过")
+
+    print("所有测试通过")