pySerial and reading binary data

Question

When the device I am communicating with sends binary data, I can recover most of it. However, there always seem to be some bytes missing, replaced by non-standard characters. For instance, one individual output looks like this:

\xc4\xa5\x06\x00.\xb3\x01\x01\x02\x00\x00\x00=\xa9

The period and equals sign should be traditional bytes in hexadecimal format (I confirmed this in another application). Other times I get other weird characters such as ')' or 's'. These characters usually occur in the exact same spot (which varies with the command I passed to the device).

How can I fix this problem?

RichieHindle · Accepted Answer · 2011-10-03 21:48:36Z

12

Are you displaying the output using something like this?:

print output

If some of your bytes happen to correspond with printable characters, they'll show up as characters. Try this:

print output.encode('hex')

to see hex values for all your bytes.

answered Oct 3, 2011 at 21:48

RichieHindle

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2 Comments

Josh Over a year ago

Thanks. This is almost two years old, but it helped me out.

RufusVS Over a year ago

print ' '.join(map(lambda x:x.encode('hex'),output)) # this separates bytes with spaces

RufusVS · Accepted Answer · 2016-03-01 21:15:09Z

2

At first I liked @RichieHindle answer, but when I tried it the hex bytes were all bunched together. To get a friendlier output, I use

print ' '.join(map(lambda x:x.encode('hex'),output))

answered Mar 1, 2016 at 21:15

RufusVS

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4 Comments

chwi Over a year ago

print(' '.join(map(lambda x:x.encode('hex',s)))) TypeError: map() requires at least two args Never used lambdas, do you have an explanation?

RufusVS Over a year ago

In RichieHindle's answer, the hex encoding is done on all the bytes of the string "output", to produce one long hex number. What my function does, is take the bytes individually from output and converts the hex, so I get the hex value of each byte, separated by spaces. lambda is an easy way to make a simple (unnamed) function for map to apply to each element of the list in the second argument to map. Learn "map" and "lambda" and you'll never go back to your old way of doing things. Trust me.

RufusVS Over a year ago

Years later, but if you found this answer and saw @chwi comment, the right-paren is misplaced in the comment.

chwi Over a year ago

So print(' '.join(map(lambda x:x.encode('hex'), s))) then :)

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