Python3 compatibility

[ikv]

Fixes python3 TabError's:

$ python3 grabserial
  File "grabserial", line 314
    if opt in ["--crtonewline"]:
                               ^
TabError: inconsistent use of tabs and spaces in indentation

Python3 renames thread to _thread, so we need to import accordingly. Also, raw_input was renamed to input.

Adds proper handling of bytes vs strings, because in python3 you cannot write bytes to stdout and strings to open('wb') file

[ikv]

@tbird20d ping?

[tbird20d]

Sorry - I had hoped to get this done before the Christmas holidays, but ran out of time.I've been out-of-the-office for the last week or so. I did take a look at portions of it, but didn't finish everything.  I read up on some of the Python 3 string/byte handling.  It looks pretty good.  I hope to get to it in the nextfew days. Thanks for the submission. -- Tim

On Wednesday, December 27, 2017, 4:02:51 PM PST, Ilya Kuzmich <notifications@github.com> wrote:  

@tbird20d ping?

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[tbird20d]

I accepted two of the patches here:

• the one for cleaning up whitespace
• the one for doing python3 imports

I rejected two of the patches here:

• the one for using #!/usr/bin/env - this has some disadvantages that I don't like, over the static, absolute path to the python binary.
• the one for changing the string handling. - All of the strings modified are in 7-bit ASCII, and are the same in all character encodings, so encoding or decoding them is not needed. Maybe I'm interpreting this wrong. Please provide this patch separately, and give some more details on why you think it is necessary, if you'd like to try to submit this again. I don't use Python3, so I don't know if this is causing some real problem, or you are just cleaning up a warning from some source analysis tool.

[tbird20d]

BTW - thanks for the patches. It inspired me to add some linters to the code, and I'm fixing a lot of source errors now. See test.sh for some tests I'm adding to my release process.

[ikv]

the one for using #!/usr/bin/env - this has some disadvantages that I don't like, over the static, absolute path to the python binary.

Why? Not every environment installs python to /usr/bin/python

Regarding strings handling: python3 str is more like python2 unicode, and python3 bytes is almost like python2 str. Grabserial receives bytes from pyserial, but stdout is in text mode, not binary, therefore writing to stdout requires decoding.