Test if byte is empty in python

Question

I'd like to test the content of a variable containing a byte in a way like this:

line = []
while True:
    for c in self.ser.read(): # read() from pySerial
        line.append(c)
        if c == binascii.unhexlify('0A').decode('utf8'):
            print("Line: " + line)
            line = []
            break

But this does not work... I'd like also to test, if a byte is empty: In this case

print(self.ser.read())

prints: b'' (with two single quotes)

I do not until now succeed to test this

if self.ser.read() == b''

or what ever always shows a syntax error...

I know, very basic, but I don't get it...

Could it simply be that you're missing the colon at the end of your if statement? Please paste a complete sample of code that is giving you a syntax error. — Arthur Tacca
– Arthur Tacca, Commented Oct 13, 2016 at 8:35
Remeber to ALWAYS include the error message you get. This helps narrowing down the possible solution and pin-point the problem. stackoverflow.com/help/how-to-ask — Floran Gmehlin
– Floran Gmehlin, Commented Oct 13, 2016 at 8:45
@Metareven I don't think so. b'' is an empty bytes, which is the correct thing to compare against. "b''" is a three character str (which in Python 2 happens to be the same thing as bytes, but we don't know what Python version is in use here). — Arthur Tacca
– Arthur Tacca, Commented Oct 13, 2016 at 10:05

fava · Accepted Answer · 2016-10-20 12:02:01Z

3

Thank you for your help. The first part of the question was answerd by @sisanared:

if self.ser.read():

does the test for an empty byte

The second part of the question (the end-of-line with the hex-value 0A) stil doesn't work, but I think it is whise to close this question since the answer to the title is given.

Thank you all

answered Oct 20, 2016 at 12:02

fava

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Comments

Kian · Accepted Answer · 2016-10-13 10:15:23Z

2

If you want to verify the contents of your variable or string which you want to read from pySerial, use the repr() function, something like:

import serial
import repr as reprlib
from binascii import unhexlify
self.ser = serial.Serial(self.port_name, self.baudrate, self.bytesize, self.parity, self.stopbits, self.timeout, self.xonxoff, self.rtscts)
line = []
while 1:
    for c in self.ser.read(): # read() from pySerial
        line.append(c)
        if if c == b'\x0A':
            print("Line: " + line)
            print repr(unhexlify(''.join('0A'.split())).decode('utf8'))
            line = []
            break

edited Oct 13, 2016 at 10:15

answered Oct 13, 2016 at 9:40

Kian

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3 Comments

Arthur Tacca Over a year ago

Why not: if c == b'\x0A': ?

Kian Over a year ago

Yes, I think it's reasonable

fava Over a year ago

while True:             print("read_line_loop")             for c in self.ser.read():                 line.append(c)                 print("appended")                 if c == b'\x0A':                     print("stop condition")                     print("Line: " + line)                     line = []                     break

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