Streamz

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import panel as pn

from streamz import Stream

pn.extension('vega')

The Streamz pane renders streamz Stream objects emitting arbitrary objects, unlike the DataFrame pane which specifically handles streamz DataFrame and Series objects and exposes various formatting objects.

Parameters:

For details on other options for customizing the component see the layout and styling how-to guides.

• always_watch (boolean, default=False): Whether to watch the stream even when not displayed.

• object (streamz.Stream): The streamz.Stream object being watched

• rate_limit (float, default=0.1): The minimum interval between events.

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The Streamz pane uses the default panel resolution to figure out the appropriate way to render the object returned by a Stream. By default the pane will only watch the Stream if it is displayed, we can tell it to watch the stream as soon as it is created by setting always_watch=True.

def increment(x):
    return x + 1

source = Stream()

streamz_pane = pn.pane.Streamz(source.map(increment), always_watch=True)

# Note: To ensure that a static render of the stream displays anything
#       we set always_watch=True and emit an event before displaying
source.emit(1)

streamz_pane

We can now define a periodic callback which emits an increasing count on the Stream:

count = 1 

def emit_count():
    global count
    count += 1
    source.emit(count)

pn.state.add_periodic_callback(emit_count, period=100, count=9);

The Streamz stream can be used to stream any kind of data, e.g. we can create a streamz DataFrame, accumulate the data into a sliding window and then map it to a altair line_plot function

import numpy as np
import altair as alt
import pandas as pd
from datetime import datetime
from streamz.dataframe import DataFrame as sDataFrame

df = sDataFrame(example=pd.DataFrame({'y': []}, index=pd.DatetimeIndex([])))

def line_plot(data):
    return alt.Chart(pd.concat(data).reset_index()).mark_line().encode(
        x='index',
        y='y',
    )

altair_stream = df.cumsum().stream.sliding_window(50).map(line_plot)

altair_pane = pn.pane.Streamz(altair_stream, height=350, always_watch=True)

for i in range(100):
    df.emit(pd.DataFrame({'y': [np.random.randn()]}, index=pd.DatetimeIndex([datetime.now()])))

altair_pane

Now we can emit additional data on the DataFrame and watch the plot update:

def emit():
    df.emit(pd.DataFrame({'y': [np.random.randn()]}, index=pd.DatetimeIndex([datetime.now()])))

pn.state.add_periodic_callback(emit, period=100, count=50);

Traceback (most recent call last):
  File "/Users/runner/work/panel/panel/panel/io/mime_render.py", line 183, in exec_with_return
    out = eval(compile(_convert_expr(last_ast.body[0]), "<ast>", "eval"), global_context)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<ast>", line 4, in <module>
NameError: name 'pn' is not defined

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