sum.py file added

Author: linxam

sum.py

@@ -0,0 +1,31 @@
+def mysum(l, start=0):
+    '''
+    sum function. Python example/exercise.
+    
+    l -> list.
+    start -> start point, that added to sum.
+    
+    function can also sum list with strings. In this case it converts 
+    all list items to str. In this case start point is - empty string
+    (c) Alexander Kilinkarov
+    '''
+    
+    # check if there is string in list. And if there is, so convert
+    # all list items to str
+    for i in l:
+        if isinstance(i, str):
+            l = map(str, l)
+            if start==0:
+                start=''
+            else:
+                start = str(start)
+            break
+            
+    # s is total sum
+    s = start
+    for i in l:
+        s+=i
+    return s
+
+print(mysum([1, 2, 3], 6))
+print(mysum(['1', '2', '3'], 'asdsa'))