BOARDS/CARDPUTER CircuitPython/sdcard_test.py

import board
import busio
import sdcardio
import storage
import os

spi = busio.SPI(board.SD_SCK, MOSI=board.SD_MOSI, MISO=board.SD_MISO)
cs = board.SD_CS

try:
    sdcard = sdcardio.SDCard(spi, cs)
    vfs = storage.VfsFat(sdcard)

    storage.mount(vfs, "/sd") # access files on sd card here
    SD_status = "SD Card Mounted"
except OSError:
    SD_status = "No SD card found"
    pass # SD card not inserted/found

print(SD_status)

# Use os to scan the SD card
files = os.listdir("/sd")
for file in files:
  print(file)
  
print("========")

# Then, reading/writing to files is as trivial as regular Python:
with open("/sd/data.txt") as f:
    lines = f.readlines()
for line in lines:
    print(line)