PIL: problem with im.show()

[Tom Kinter]

system configuration
  Sun Solaris-2.6
  python-1.5.2
  PIL-1.0

in PIL/libImaging, the following step suggested in the installation works:
  make check

in PIL/Scripts the following scripts were tried and worked:
  python viewer.py lena.ppm
  python thresholder.py lena.ppm
  python enhancer.py lena.ppm
  python painter.py lena.ppm

the following interactive process 
>>> import Image
>>> im = Image.open("lena.ppm")
>>> print im.format, im.size, im.mode
PPM (128, 128) RGB
>>> im.show()
Traceback (innermost last):
  File "<stdin>", line 1, in ?
  File "/usr/local/lib/python1.5/site-packages/PIL/Image.py", line 694, in show
    _showxv(self, title, command)
  File "/usr/local/lib/python1.5/site-packages/PIL/Image.py", line 974, in _showxv
    file = self._dump(format=format)
  File "/usr/local/lib/python1.5/site-packages/PIL/Image.py", line 311, in _dump
    file = file + "." + format
TypeError: illegal argument type for built-in operation
>>> 

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Tom Kinter     tmk at mayo.edu     507-284-4981
     Mayo Foundation Rochester MN 55905 USA
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