Watch logfile and draw it online


I want constantly read data from file at the same time as this file is written by other service (something like tail -f file.log) and draw results. How draw it, I undestand: dash_core_components.Interval

I wanna do it without using queries brokers like redis etc, Is it possible?

Hi! I’m doing a similar thing with .csv files. For me it’s not being a problem using .Interval as an input in a callback, pandas.readcsv inside the callback function, and the figure of the chart in the output.


Hey! Did you manage to do it? I can’t find a way to auto-scroll to last line added (in order to print new logs)

One approach might be to Store the latest file position after each update. Then, you could do something like the following within the callback:

latest_position = my_tail_store

new_data = pd.DataFrame()
with open(filename, 'r') as fin:
    #skip to the latest read position before beginning processing remaining lines, latest_position)

    # process line by line until eof
    for line in fin:
        # do something with each line that will prepare it for visualization in dash
        row = myparser.parse_logmessage(line.strip())
        # ... aggregate it to use once the file has been closed

    # record the current file.EOF
    latest_position = fin.tell()

# let's assume you have dash 0.38 rc1 installed, supporting multiple outputs in callbacks
return latest_position, new_data

If you’re just printing log message into a pre/div you could skip the read-by-line parsing stuff.

1 Like

this fit perfectly with the new multi output.

Thanks :slight_smile: