Gpiozero: Disk usage internal device

[bennuttall]

df -h as an internal device.

[jee1mr]

@bennuttall can I take this up too?

[bennuttall]

Go for it :+1:

Don't PR it just yet - I'm adding tests and changing things in that file. If you just create a new class you can paste in later on that should be great.

It should take an argument which defaults to / for which drive it's looking at.

I was going to build on this: https://github.com/bennuttall/piwheels/blob/227648a1e8296f676da9c93816ba9355d12e8b75/piwheels/tools.py#L37:L40

[jee1mr]

class DiskUsage(InternalDevice):
    """
    Extends :class:`InternalDevice` to provide a device which is active when
    the disk free space exceeds the *threshold* value.

    :param str filesystem:
        The filesystem for which the disk usage needs to be computed. This
        defaults to `/`, which is the root filesystem. 

    :param float threshold:
        The disk usage percentage above which the device will be considered "active".
        This defaults to 90.0.
    """
    def __init__(self, filesystem='/', threshold=90.0):
        super(DiskUsage, self).__init__()
        if not os.path.exists(filesystem):
            raise ValueError('invalid filesystem')
        self.filesystem = filesystem
        self.threshold = threshold
        self._fire_events()

    def __repr__(self):
        return '<gpiozero.DiskUsage usage=%.2f%%>' % self.usage

    @property
    def usage(self):
        """
        Returns the current disk usage in percentage.
        """
        df = subprocess.Popen(['df', '-h', self.filesystem], stdout=subprocess.PIPE)
        output = df.communicate()[0].split()
        return float(output[11].decode('UTF-8').rstrip('%'))

    @property
    def is_active(self):
        """
        Returns ``True`` when the Disk :attr:`usage` exceeds the
        :attr:`threshold`.
        """
        return self.usage > self.threshold

@bennuttall Does it look good?

[lurch]

I think the docstring needs changing from "a device which is active when the disk free space exceeds the threshold value" to "a device which is active when the disk space used exceeds the threshold value" ?

Might be worth splitting on newlines _before_ splitting on whitespace, in case the column headers have a different number of spaces in different languages? (although a quick skim of df --help suggests df --output=pcent <filesystem> might be easier? :wink: )

Perhaps it's also worth providing a value property which is simply the usage % re-scaled from 0-100 to 0-1? (which then means it would plug in nicely with sourcetools, e.g. have a LED bargraph displaying how full your disk is :slightly_smiling_face: )

[bennuttall]

Thanks both - @jee1mr can you PR this with @lurch's changes? Against internal-devices if it's not merged yet.

[jee1mr]

@lurch Thanks for the suggestions :)
@bennuttall Will do.