Calculating several cells into one cell in same table using ArcPy

Question

I'm very new to Python and scripting in ArcGIS. I need to calculate some cells from one field in table into another one cell in another field in same table.

Here's what i need:

Here's what i try and it doesnt work.

A = arcpy.da.SearchCursor("S2_merge2", ["Name1"] , 'FID = 0')
B = arcpy.da.SearchCursor("S2_merge2", ["Name1"] , 'FID = 1')
C = arcpy.da.SearchCursor("S2_merge2", ["Name1"] , 'FID = 2')

cursor = arcpy.da.UpdateCursor("S2_merge2", ["Name5"] , FID = 0')

for row in cursor:      
    row[0] = A+B+C   
    cursor.updateRow(row)

Answer 1

first copy the column "Name1" in a python list

features = [[row[0] for row in arcpy.da.SearchCursor("S2_merge2", ("Name1") )]

then use the indices with your search cursor (note that I use a selection to avoid troubles with the last 2 rows, as you did not tell how to manage those)

cursor = arcpy.da.UpdateCursor("S2_merge2", ["Name5"],  'FID < ' + str(int(arcpy.GetCount_management("S2_merge2").getOutput(0))-2) )

i=0
for row in cursor:      
    row[0] = features[i] + features[i+1] + features[i+2]
    cursor.updateRow(row)
    i+=1

with a single row :

fid_val = 42 #42 is just an example
cursor = arcpy.da.UpdateCursor("S2_merge2", ["Name5"],  'FID = ' + str(fid_val) )


for row in cursor:      
    row[0] = features[fid_val] + features[fid_val+1] + features[fid_val+2]
    cursor.updateRow(row)