circuitpython/tests/extmod/vfs_fat_fileio1.py

try:
    import uerrno
    import uos
except ImportError:
    print("SKIP")
    raise SystemExit

try:
    uos.VfsFat
except AttributeError:
    print("SKIP")
    raise SystemExit


class RAMFS:

    SEC_SIZE = 512

    def __init__(self, blocks):
        self.data = bytearray(blocks * self.SEC_SIZE)

    def readblocks(self, n, buf):
        # print("readblocks(%s, %x(%d))" % (n, id(buf), len(buf)))
        for i in range(len(buf)):
            buf[i] = self.data[n * self.SEC_SIZE + i]

    def writeblocks(self, n, buf):
        # print("writeblocks(%s, %x)" % (n, id(buf)))
        for i in range(len(buf)):
            self.data[n * self.SEC_SIZE + i] = buf[i]

    def ioctl(self, op, arg):
        # print("ioctl(%d, %r)" % (op, arg))
        if op == 4:  # MP_BLOCKDEV_IOCTL_BLOCK_COUNT
            return len(self.data) // self.SEC_SIZE
        if op == 5:  # MP_BLOCKDEV_IOCTL_BLOCK_SIZE
            return self.SEC_SIZE


try:
    bdev = RAMFS(50)
except MemoryError:
    print("SKIP")
    raise SystemExit

uos.VfsFat.mkfs(bdev)
vfs = uos.VfsFat(bdev)
uos.mount(vfs, "/ramdisk")
uos.chdir("/ramdisk")

# file IO
f = open("foo_file.txt", "w")
print(str(f)[:17], str(f)[-1:])
f.write("hello!")
f.flush()
f.close()
f.close()  # allowed
try:
    f.write("world!")
except OSError as e:
    print(e.errno == uerrno.EINVAL)

try:
    f.read()
except OSError as e:
    print(e.errno == uerrno.EINVAL)

try:
    f.flush()
except OSError as e:
    print(e.errno == uerrno.EINVAL)

try:
    open("foo_file.txt", "x")
except OSError as e:
    print(e.errno == uerrno.EEXIST)

with open("foo_file.txt", "a") as f:
    f.write("world!")

with open("foo_file.txt") as f2:
    print(f2.read())
    print(f2.tell())

    f2.seek(0, 0)  # SEEK_SET
    print(f2.read(1))

    f2.seek(0, 1)  # SEEK_CUR
    print(f2.read(1))
    f2.seek(2, 1)  # SEEK_CUR
    print(f2.read(1))

    f2.seek(-2, 2)  # SEEK_END
    print(f2.read(1))

# using constructor of FileIO type to open a file
# no longer working with new VFS sub-system
# FileIO = type(f)
# with FileIO("/ramdisk/foo_file.txt") as f:
#    print(f.read())

# dirs
vfs.mkdir("foo_dir")

try:
    vfs.rmdir("foo_file.txt")
except OSError as e:
    print(e.errno == 20)  # uerrno.ENOTDIR

vfs.remove("foo_file.txt")
print(list(vfs.ilistdir()))