trend¶

Trends of tile values: rising or falling over up to three hours.

The board keeps a short history per source itself, so trends work with any data source and cost no extra request: at most one sample every SAMPLE_INTERVAL_S, dropped once older than SPAN_S. It does so for every number tile, so an arrow can appear as soon as a tile’s trend is switched on. A trend compares the current value with the oldest sample: in steady operation one from three hours ago, after a restart the oldest there is, so a trend shows up within half an hour.

The history is a dict {source ID: [[time s, value], …]}, oldest first, stored as JSON on flash between wakes (HISTORY_FILE); it only changes when a sample is added, so the file is written at most every half hour.

Attributes¶

`HISTORY_FILE`
`SAMPLE_INTERVAL_S`
`SPAN_S`
`SLACK_S`
`UP`
`DOWN`

Functions¶

`record`(history, readings, sources, now_s)	Add the current values of `sources` to `history`.
`direction`(samples, value, now_s, threshold)	Return UP, DOWN or None (steady, or no older value yet).
`sources`(tile_config)	Source IDs to keep a history for: those of number tiles, each once.
`annotate`(layout_tiles, history, readings, now_s)	Set "arrow" (UP, DOWN or None) on layout tiles that have a "trend".
`load`([path])	Return the saved history, or an empty one.
`save`(history[, path])	Store the history; a power cut leaves the previous file intact.

Module Contents¶

trend.HISTORY_FILE = 'trend.json'¶

trend.SAMPLE_INTERVAL_S = 1800¶

trend.SPAN_S = 10800¶

trend.SLACK_S = 60¶

trend.UP = 'up'¶

trend.DOWN = 'down'¶

trend.record(history, readings, sources, now_s)¶

Add the current values of sources to history.

Parameters:

history – The previous history, or None.
readings – Current readings {source ID: {“value”: …}}.
sources – Source IDs to keep a history for.
now_s – Current time in seconds.

Returns:

The new history; sources no longer asked for are dropped.

trend.direction(samples, value, now_s, threshold)¶

Return UP, DOWN or None (steady, or no older value yet).

Parameters:

samples – The history of one source (see record).
value – The current value.
now_s – Current time in seconds.
threshold – Smallest change that counts as a trend.

trend.sources(tile_config)¶: Source IDs to keep a history for: those of number tiles, each once.

trend.annotate(layout_tiles, history, readings, now_s)¶

Set “arrow” (UP, DOWN or None) on layout tiles that have a “trend”.

Parameters:

layout_tiles – Tiles as tiles.to_layout returns them; changed in place.
history – The history (see record).
readings – Current readings {source ID: {“value”: …}}.
now_s – Current time in seconds.

trend.load(path=HISTORY_FILE)¶: Return the saved history, or an empty one.

trend.save(history, path=HISTORY_FILE)¶: Store the history; a power cut leaves the previous file intact.