Opening serial ports¶
Open port at “9600,8,N,1”, no timeout:
>>> import serial >>> ser = serial.Serial('/dev/ttyUSB0') # open serial port >>> print(ser.name) # check which port was really used >>> ser.write(b'hello') # write a string >>> ser.close() # close port
Open named port at “19200,8,N,1”, 1s timeout:
>>> with serial.Serial('/dev/ttyS1', 19200, timeout=1) as ser: ... x = ser.read() # read one byte ... s = ser.read(10) # read up to ten bytes (timeout) ... line = ser.readline() # read a '\n' terminated line
Open port at “38400,8,E,1”, non blocking HW handshaking:
>>> ser = serial.Serial('COM3', 38400, timeout=0, ... parity=serial.PARITY_EVEN, rtscts=1) >>> s = ser.read(100) # read up to one hundred bytes ... # or as much is in the buffer
Configuring ports later¶
Get a Serial instance and configure/open it later:
>>> ser = serial.Serial() >>> ser.baudrate = 19200 >>> ser.port = 'COM1' >>> ser Serial<id=0xa81c10, open=False>(port='COM1', baudrate=19200, bytesize=8, parity='N', stopbits=1, timeout=None, xonxoff=0, rtscts=0) >>> ser.open() >>> ser.is_open True >>> ser.close() >>> ser.is_open False
Also supported with context manager:
with serial.Serial() as ser: ser.baudrate = 19200 ser.port = 'COM1' ser.open() ser.write(b'hello')
readline() reads up to one line, including the
\n at the end.
Be careful when using
readline(). Do specify a timeout when opening the
serial port otherwise it could block forever if no newline character is
received. If the
\n is missing in the return value, it returned on timeout.
readlines() tries to read “all” lines which is not well defined for a
serial port that is still open. Therefore
readlines() depends on having
a timeout on the port and interprets that as EOF (end of file). It raises an
exception if the port is not opened correctly. The returned list of lines do
not include the
Both functions call
read() to get their data and the serial port timeout
is acting on this function. Therefore the effective timeout, especially for
readlines(), can be much larger.
Do also have a look at the example files in the examples directory in the source distribution or online.
eol parameter for
readline() is no longer supported when
pySerial is run with newer Python versions (V2.6+) where the module
io is available.
To specify the EOL character for
readline() or to use universal newline
mode, it is advised to use io.TextIOWrapper:
import serial import io ser = serial.serial_for_url('loop://', timeout=1) sio = io.TextIOWrapper(io.BufferedRWPair(ser, ser)) sio.write(unicode("hello\n")) sio.flush() # it is buffering. required to get the data out *now* hello = sio.readline() print(hello == unicode("hello\n"))
python -m serial.tools.list_ports will print a list of available ports. It
is also possible to add a regexp as first argument and the list will only
include entries that matched.
The enumeration may not work on all operating systems. It may be incomplete, list unavailable ports or may lack detailed descriptions of the ports.