Serial read & write using Arduino and Python

I'm trying to write a command to my COM PORT but the write method won't take my string

I expected a text file to be written by reading directly from the Arduino Nano 33 IoT with an inertial measurement unit LSM6DS3. However, the Python script gets stuck at write stage, so the line 'Data Acquisition started" does not write, and no data is read to the text file. Can anybody please help?

Python

# -----------------------------------------------------------------------------
# Import Standard Libraries
# -----------------------------------------------------------------------------
import numpy as np
import serial
import time
import os
# -----------------------------------------------------------------------------
# Definition of Directories
# -----------------------------------------------------------------------------
out_dir = # some generic path
# -----------------------------------------------------------------------------
# Definition of Parameters
# -----------------------------------------------------------------------------
# Serial Port
port = 'COM4' # Arduino Serial Port
b_rate = 38400 # Serial Baud Rate
# Test
T = 5 # Test Time (s)
test_id = 'A_0456_001' # Test ID
# -----------------------------------------------------------------------------
# Open Serial Port
# -----------------------------------------------------------------------------
ard = serial.Serial(port,b_rate)
time.sleep(1)
# -----------------------------------------------------------------------------
# Acquire Data
# -----------------------------------------------------------------------------
# Create Output Text File
out_path = os.path.join(out_dir,test_id + '.txt')
if os.path.exists(out_path):
os.remove(out_path)
out_file = open(out_path,'w')
# Start Arduino
ard.write(str.encode('s'))
print('Data aquisition started...')
time.sleep(1)
t_0 = time.time_ns()
t_c = t_0
p_count = 0
while t_c < t_0 + T*10**9:
# Write Header
if p_count == 0:
header = 'System Time, Type, ard_time, x, y, z'
out_file.write(header + '\n')
# Read Serial
s_line = ard.readline()
t_c = time.time_ns() # High precision time
# Write data to text file
out_file.write(str(t_c) + ',' + str(s_line)[2:-5] + '\n')
p_count = p_count+1
print('Data aquisition ended.')
# Stop Arduino and close serial
ard.write(str.encode('e'))
ard.close()
# Close Text File
out_file.close()

Arduino

#include <Arduino_LSM6DS3.h>
void setup() {
Serial.begin(9600);
while (!Serial);
if (!IMU.begin()) {
Serial.println("Failed to initialize IMU!");
while (1);
}
Serial.print("Accelerometer sample rate = ");
Serial.print(IMU.accelerationSampleRate());
Serial.println(" Hz");
Serial.println();
Serial.println("Acceleration in G's");
Serial.println("X\tY\tZ");
}
void loop() {
float x, y, z;
if (IMU.accelerationAvailable()) {
IMU.readAcceleration(x, y, z);
Serial.print(x,5);
// 5 decimal places
Serial.print('\t');
Serial.print(y,5);
Serial.print('\t');
Serial.println(z,5);
}
}

The problem you are facing is with your write command in the python portion of the code.

The encode() function's argument is the encoding (default is UTF-8) and not the string to encode. This should then be applied to the string you are sending. Like this:

-----
# Start Arduino
ard.write('s'.encode())
print('Data aquisition started...')
time.sleep(1)
-----