PySerial. Why does an error occur when writing to the COM port?

Question

Python

Here it was necessary to write a simple script for communication with the modem. I installed the PySerial library, and when I try to write to the port, I get the following bug report:

import serial
>>> ser = serial.Serial('COM4', baudrate=115200, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS, xonxoff=1)
>>> ser.write("at")
Traceback (most recent call last):
  File "<pyshell#13>", line 1, in <module>
    ser.write("at")
  File "C:\Python34\lib\site-packages\serial\serialwin32.py", line 283, in write
    data = to_bytes(data)
  File "C:\Python34\lib\site-packages\serial\serialutil.py", line 76, in to_bytes
    b.append(item)  # this one handles int and str for our emulation and ints for Python 3.x
TypeError: an integer is required
ser.open()
>>> ser.isOpen()
True
>>> ser.write('AT')
Traceback (most recent call last):
  File "<pyshell#30>", line 1, in <module>
    ser.write('AT')
  File "C:\Python34\lib\site-packages\serial\serialwin32.py", line 283, in write
    data = to_bytes(data)
  File "C:\Python34\lib\site-packages\serial\serialutil.py", line 76, in to_bytes
    b.append(item)  # this one handles int and str for our emulation and ints for Python 3.x
TypeError: an integer is required
>>>

What could I have done wrong?
Windiws 8.1 system, Python 3.4, PySerial 2.6. In the terminal, the port is perfectly opened, written and read.

Answer 1

Perhaps because the port needs to be opened first. stackoverflow.com/questions/676172/full-examples-o...
Try writing as a byte string:
ser.write(b"at")

Answer 2

In general, he says that he expects a number.
try writing like this:
ser.write("AT".encode('cp1251'))
Also, try to close the port first, and then open it. those. at the beginning of the script ser.close() then ser.open()
Try to set a timeout in the port settings. timeout=5 (for example)