micropython/examples/accellog.py

# log the accelerometer values to a .csv-file on the SD-card

import pyb

accel = pyb.Accel()  # create object of accelerometer
blue = pyb.LED(4)  # create object of blue LED

# open file to write data - /sd/ is the SD-card, /flash/ the internal memory
log = open("/sd/log.csv", "w")

blue.on()  # turn on blue LED

# do 100 times (if the board is connected via USB, you can't write longer because the PC tries to open the filesystem which messes up your file.)
for i in range(100):
    t = pyb.millis()  # get time since reset
    x, y, z = accel.filtered_xyz()  # get acceleration data
    log.write("{},{},{},{}\n".format(t, x, y, z))  # write data to file

log.close()  # close file
blue.off()  # turn off LED