add some restriction

git-svn-id: https://pdfminerr.googlecode.com/svn/trunk/pdfminer@22 1aa58f4a-7d42-0410-adbc-911cccaed67c

lzw.py

@@ -17,7 +17,6 @@ class LZWDecoder:
     return
 
   def readbits(self, bits):
-    bits0 = bits
     v = 0
     while 1:
       # the number of remaining bits we can get from the current buffer.

pdf2txt.py

@@ -163,11 +163,14 @@ class TextConverter(PDFDevice):
 
 
 # pdf2txt
+class TextExtractionNotAllowed(RuntimeError): pass
 def pdf2txt(outfp, rsrc, fname, pages, codec, debug=0):
   device = TextConverter(rsrc, debug=debug)
   doc = PDFDocument(debug=debug)
   fp = file(fname)
   parser = PDFParser(doc, fp, debug=debug)
+  if not doc.is_extractable:
+    raise TextExtractionNotAllowed('text extraction is not allowed: %r' % fname)
   interpreter = PDFPageInterpreter(rsrc, device, debug=debug)
   outfp.write('<document>\n')
   for (i,page) in enumerate(doc.get_pages(debug=debug)):