finding max (#1488)

* Update find_max.py

* Update find_max.py

* Format with psf/black and add doctests

Author: Deekshaesha

maths/find_max.py

@@ -2,15 +2,23 @@
 
 
 def find_max(nums):
+    """
+    >>> for nums in ([3, 2, 1], [-3, -2, -1], [3, -3, 0], [3.0, 3.1, 2.9]):
+    ...     find_max(nums) == max(nums)
+    True
+    True
+    True
+    True
+    """
     max = nums[0]
     for x in nums:
         if x > max:
             max = x
-    print(max)
+    return max
 
 
 def main():
-    find_max([2, 4, 9, 7, 19, 94, 5])
+    print(find_max([2, 4, 9, 7, 19, 94, 5]))  # 94
 
 
 if __name__ == "__main__":