add summation

chapter4/summation.py

@@ -0,0 +1,13 @@
+class Number:
+    def __init__(self, value):
+        self.value = value
+
+
+def summation(nums):
+    if len(nums) == 1:
+        return nums[0].value
+    return nums[0].value + summation(nums[1:])
+
+
+nums = [Number(i) for i in range(0, 100, 3)]
+print(summation(nums))