How to read from serial port?

[Peter Otten]

David Aldrich wrote:

> Hi
> 
> I have written a very simple program to read and print data from the
> serial port using pyserial:
> 
> #!/usr/bin/python3
> import serial
> 
> ser=serial.Serial('COM1',115200)
> while True:
>     out = ser.read()
>     print('Receiving...'+out)
> 
> When I run it and send data for it to read I get:
> 
> C:\SVNProj\Raggio\trunk\hostconsole\gui\prototypes\serial_test>py
> serial_read.py Traceback (most recent call last):
>   File "serial_read.py", line 9, in <module>
>     print('Receiving...'+out)
> TypeError: Can't convert 'bytes' object to str implicitly
> 
> I am using Python 3.5.  How would I fix this error please?

Look at the traceback again. The line

>     out = ser.read()

is executed, you are reading successfully. What fails is

>     print('Receiving...'+out)

You are trying to concatenate a (unicode) string and bytes, like in

>>> print("foo" + b"bar")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Can't convert 'bytes' object to str implicitly

You can avoid that by printing the string and the bytes independently

>>> print("foo", b"bar")
foo b'bar'

If you don't like the b"..." stuff and want to treat the bytes as text 
rather than data you can decode them:

>>> print("foo", b"bar".decode())
foo bar

For more see <https://docs.python.org/3/howto/unicode.html>.