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tannewt opened this issue Sep 8, 2017 · 5 comments · Fixed by #932
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os.listdir inconsistent #249

tannewt opened this issue Sep 8, 2017 · 5 comments · Fixed by #932
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3.0

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@tannewt
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tannewt commented Sep 8, 2017

After an SD card is mounted, os.listdir returns different results depending on if the path name is given or implicit through the current working directory.

print(os.listdir(os.getcwd()))
print(os.listdir())

Produces:

[b'sd', 'boot_out.txt', '.fseventsd', 'adafruit_sdcard.mpy', 'code.py', '._code.py', 'adafruit_bus_device']
['boot_out.txt', '.fseventsd', 'adafruit_sdcard.mpy', 'code.py', '._code.py', 'adafruit_bus_device']
@tannewt tannewt added this to the 3.0 milestone Oct 25, 2017
@stewmystre stewmystre mentioned this issue Nov 28, 2017
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@tannewt tannewt added the bug label Jan 16, 2018
@RidleyLarsen
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I'm going to take a look at this.

@RidleyLarsen
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This is a little outside my comfort zone (which is great!) but I'm reading through the C code. My first intuition is that when the listdir function has to infer the directory, it's not recognizing it as the root directory in the way it would when you explicitly provide it with the root directory (via getcwd()).

@dhalbert
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It turns out the reason for this has to do with what's mounted where, and how MicroPython was set up to handle mounted filesystems. On the pyboard, the internal flash is mounted as /flash, and an SD card is mounted as /sd:

>>> os.listdir('/')
['flash', 'sd']

On the pyboard, / is not a filesystem: it's only a location for mount points. On the pyboard, you cannot create files or directories in /:

>>> f = open("/foo.txt", 'w')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 19] ENODEV
>>> os.mkdir('/mnt')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 19] ENODEV

The assumption that / is only for mount points is carried through in mp_vfs_lookup_path(), which is called indirectly by os.listdir(). In CircuitPython we mount the the on-board filesystem (CIRCUITPY) on /, not someplace like /flash or /circuitpy. So the fix is probably to make mp_vfs_lookup_path be more flexible.

@deshipu
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deshipu commented Jun 15, 2018

I don't know if this belongs here, but we also had a user report that if you create a directory called sd and also mount the sdcard as sd, you get "sd" listed twice by listdir.

@dhalbert
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@deshipu, hmm, that's another bug. It should not let you use a mount point that's the same name as an existing file or dir.

@dhalbert dhalbert mentioned this issue Jun 15, 2018
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fix os.listdir() when current dir is '/' dhalbert/circuitpython
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@tannewt @deshipu @dhalbert @RidleyLarsen
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