KeyError: '13'

[Phanindra Ramesh Challa]

I am trying to run a python program. It is giving the KeyError: '13'. I
have no clue regarding this error.
 this is the python code relevant to the error:

dpi = 100
bold = 0
italic = 0
mono = 0
comment = ""
dbname = "font.db"

for o, a in opts:
if o == '-b': bold = 1
if o == '-i': italic = 1
if o == '-m': mono = 1
if o == '-d': dpi = int (a)
if o == '-c': comment = string.join (string.split (a), " ")
if o == '-g': dbname = a

fontname = args[0]
pixel_size = int (args[1])

point_size = int (pixel_size * 72.27 / dpi + 0.5)

# Approximate average glyph width.
avg_width = pixel_size * 17 / 24

db = anydbm.open (dbname, "r")
codes = loads (db [str (pixel_size)])

And the error is :
python2 ../../../mk_bdf.py -c "Converted from fonts of Computer Modern
family (C) 1979-1985 Donald E. Knuth and others." -b  'TeX Sans' 13 >
tex09sb.bdf
Traceback (most recent call last):
  File "../../../mk_bdf.py", line 108, in <module>
    codes = loads (db [str (pixel_size)])
  File "/usr/lib/python2.7/bsddb/__init__.py", line 270, in __getitem__
    return _DeadlockWrap(lambda: self.db[key])  # self.db[key]
  File "/usr/lib/python2.7/bsddb/dbutils.py", line 68, in DeadlockWrap
    return function(*_args, **_kwargs)
  File "/usr/lib/python2.7/bsddb/__init__.py", line 270, in <lambda>
    return _DeadlockWrap(lambda: self.db[key])  # self.db[key]
KeyError: '13'



 Anybody please help me in running the program.
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