ArcGIS Field Calculator Python numbering rows of fishnet

I have a grid of 100*100 cells. I want to add to each cell a number representing the row it is in (like in excel). I added a field and want try to solve that with field calculator:

The code is something like this:

def test( OBJECTID ):

 if OBJECTID > 0 and OBJECTID < 101:
     return 1


 elif OBJECTID > 100 and OBJECTID < 201:
     return 2

 elif OBJECTID > 200 and OBJECTID < 301:
     return 3

 elif OBJECTID > 300 and OBJECTID < 401:
     return 4

 elif OBJECTID > 400 and OBJECTID < 501:

     return 5

 elif  OBJECTID > 500 and OBJECTID < 601:
     return 6

 elif  OBJECTID > 600 and OBJECTID < 701:
     return 7

This works good, however I want to automate it a little bit. The return value shall automatically be counted to the next number.

I tried to solve this with autoincrement. Though it adds a number per cell and not per row. Any ideas how to solve that?

Meanwhile I figured, that the cells of each row have obviously the same coordinates and with the help of another guy I have now this code. However I receive only NULL values for the fields. Any ideas what is wrong

def test( X_KORD_ED ):
    var = 0
    old_i = object() 

    for i in X_KORD_ED: 
        if i != old_i:
            var += 1
            old_i = i
        yield i, var

Answer

Thanks for the answers. I solved the problem via the coordiantes of the cells/polygons. I summarized the x and y coordinate, exported it to excel, added 1-100 and ABC and joined it back to the feature class.