Python3000
    A mythical python release, not required to be backward compatible, 
    with telepathic interface.

Zen of Python
    Listing of Python design principles and philosophies that are 
    helpful in understanding and using the language. The listing 
    can be found by typing ``import this'' at the interactive prompt.

Было:

rows    = []
cols    = []
            
for key in values.keys():
     row, col = key
                
     if not col in cols: cols.append(col)
     if not row in rows: rows.append(row)
        
n_rows = max(rows)
n_cols = max(cols)


Стало:

n_rows  = 0
n_cols  = 0
            
for key in values.keys():
    row, col = key

    if row > n_rows: n_rows = row
    if col > n_cols: n_cols = col