human
Solve the following python programming problem given the following code:
def make_canvas(txt, attr, maxcol, fill_attr = None) : 
    processed_txt = [] 
    processed_attr = [] 
    processed_cs = [] 
    for (line, line_attr) in zip (txt, attr) : 
        line_attr = [(aname, l) for (aname, l) in line_attr if (l > 0)] 
        diff = (maxcol - len (line_attr)) 
        if (diff > 0) : 
            line += (' ' * diff) 
            line_attr.append ((fill_attr, diff)) 
else : 
            from urwid.util import rle_subseg 
            line = line [: maxcol] 
            line_attr = rle_subseg (line_attr, 0, maxcol) 
from urwid.util import apply_target_encoding 
        (encoded_line, line_cs) = apply_target_encoding (line) 
        def get_byte_line_attr(line, line_attr) : 
            i = 0 
            for (label, column_count) in line_attr : 
                byte_count = len (line [i : (i + column_count)].encode (_target_encoding)) 
                i += column_count 
                (yield (label, byte_count)) 
line_attr = list (get_byte_line_attr (line, line_attr)) 
        processed_txt.append (encoded_line) 
        processed_attr.append (line_attr) 
        processed_cs.append (line_cs) 
return urwid.TextCanvas (processed_txt, processed_attr, processed_cs, maxcol = maxcol) 

    
    

    Fix the buggy line: diff = (maxcol - len (line_attr))
assistant
#Here is Python program to fix the buggy line: diff = (maxcol - len (line_attr))
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diff = (maxcol - len (line))