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  1. import io
  2.  
  3. def read_last_line(file, buffer_size=128, nlchar="\n"):
  4.     offset = max(file.seek(0, 2) - buffer_size, 0)
  5.     file.seek(file.seek(0, 2) - len(nlchar))
  6.  
  7.     while True:
  8.         file.seek(offset)
  9.         buffer = file.read(buffer_size)
  10.         try:
  11.             i = buffer.rindex(nlchar)
  12.         except ValueError:
  13.             if offset == 0:
  14.                 break
  15.             offset = max(offset - buffer_size, 0)
  16.             continue
  17.         file.seek(offset+i+len(nlchar))
  18.         return file.read()
  19.     file.seek(0)
  20.     return file.read()
  21.  
  22. tests = [
  23. 	io.StringIO("single line"),
  24. 	io.StringIO("line\nlast"),
  25. 	io.StringIO("line\nlast\n"),
  26. 	io.StringIO("\n".join(str(n) for n in range(1000))),
  27. ]
  28. for i, test in enumerate(tests):
  29. 	ll1 = test.readlines()[-1]
  30. 	ll2 = read_last_line(test)
  31. 	print(f"{i+1:2d}. {ll1!r} {ll2!r} {ll1==ll2}")
Success #stdin #stdout 0.08s 14064KB
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Standard input is empty
stdout
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 1. 'single line' 'single line' True
 2. 'last' 'last' True
 3. 'last\n' '' False
 4. '999' '999' True
https://ideone.com/jvPRFQ
language:
Python 3 (python  3.12)
created:
15 hours ago
visibility:
public

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