Drawing Charts

The CanvasXpress object defines what a chart should contain and how it should be formatted, but rendering the chart is performed by the functions graph() and show_in_browser().

To use graph() import it from canvasxpress.plot and then call it by passing a CanvasXpress object. For example, a Quarto, RMD, or Jupyter Notebook code chunk could be:

from random import random

from canvasxpress.canvas import CanvasXpress
from canvasxpress.plot import graph

graph(
    CanvasXpress(
        data={
            "y": {
                "data": [
                    [random() % 100 for i in range(20)]
                ],
                "vars": ["A"],
            }
        },
        config={
            "background": "rgb(255,255,255)",
            "colorScheme": "CanvasXpress",
            "graphOrientation": "vertical",
            "graphType": "Area",
            "objectBorderColor": False,
            "plotBox": False,
            "plotBoxColor": "rgb(204,204,204)",
            "showLegend": False,
            "showLegendBorder": True,
            "smpLabelRotate": 90,
            "smpTitle": "time",
            "xAxis": ["A"],
            "xAxisTickRightShow": False,
            "yAxisTickTopShow": False
        },
        width=609,
        height=609
    )
)

Some application frameworks, such as Shiny for Python and Plotly Dash, expect an object to be rendered to the framework as part of the reactive flow. In these contexts, the graph() function creates an appropriate object and returns it. That value can be assigned to a variable to be returned at a later point in the code, or be immediately returned. See the Shiny for Python and Dash examples for specific usage.

show_in_browser() is similar to graph() except that it opens a browser window on the local system and displays the chart. It's used to facilitate learning and debugging.

graph() does a good job of determining the runtime context to choose how the chart should be rendered, but in the case installed packages or runtime configurations confuse the function an environment variable can be set to override how graph() performs the rendering. Set CANVASXPRESS_TARGET_CONTEXT to be one of these values as appropriate for this situation (and don't forget to pip install the necessary package support):

• rstudio
• shiny
• jupyter
• dash
• streamlit
• browser

For example:

from os import environ

environ["CANVASXPRESS_TARGET_CONTEXT"] = "jupyter"

or via a shell (bash example provided):

export CANVASXPRESS_TARGET_CONTEXT="jupyter"

Example Agent Prompts

The CanvasXpress AI skills enable you to generate production-ready chart code using natural language prompts. Below are example prompts you can use with AI coding assistants:

Bar Charts

Prompt: "Create a vertical bar chart using CanvasXpress showing monthly sales data. The x-axis should display 5 categories labeled Jan through May. The y-axis shows sales values: 120, 150, 180, 200, 250. Title the chart 'Monthly Sales' and set dimensions to 600x600 pixels."

Prompt: "Generate a horizontal bar chart comparing two variables (Var 1 and Var 2) across five categories (Cat 1 through Cat 5). Display the data values inside each bar in white text. Use a blue color scheme with the title 'Bar Graph Showing Data Values'. The chart should be 600x600 pixels."

Heatmaps

Prompt: "Create a heatmap visualization of gene expression data with 3 genes (GeneA, GeneB, GeneC) and 3 samples (Sample1, Sample2, Sample3). Use a diverging color scheme. Display the title 'Gene Expression Heatmap' and add a subtitle 'Relative Expression Levels'. Set dimensions to 600x600 pixels."

Scatter Plots

Prompt: "Generate a scatter plot showing the relationship between two continuous variables. The x-axis represents 'Age' (values 20-60) and the y-axis represents 'Response' (values 10-100). Add a regression line, label both axes, and title the chart 'Age vs Response Relationship'. Use a blue color scheme with circular markers. Dimensions: 600x600."

Multi-Series Charts

Prompt: "Create a grouped bar chart showing sales data for three products (Product A, Product B, Product C) across six months (Jan-Jun). Group the bars by month and use distinct colors for each product. Display a legend at the bottom with 3 columns. Add axis labels and title 'Product Sales by Month'. Set dimensions to 600x600 pixels."

Tips for Effective Prompts

When crafting your prompts, include:

• Chart type: Specify the desired chart (bar, heatmap, scatter, line, etc.)
• Data description: Describe your data structure (categories, values, variables)
• Visual preferences: Mention colors, themes, dimensions, axis labels
• Special features: Note if you need legends, annotations, or data values

The AI agent will validate the generated code for syntax correctness before presenting it to you.

Default and Pinned CanvasXpress JavaScript Editions

CanvasXpress for Python generates JavaScript that assumes use of the latest available edition of CanvasXpress for JavaScript, but it can be set to use a specific edition.

Review this site for available versions: https://cdnjs.com/libraries/canvasXpress

The desired version is expressed as a str. Prior to generating a CanvasXpress chart use the following code to set the edition that shall be used:

from canvasxpress.canvas import CanvasXpress

CanvasXpress.set_cdn_edition("48.3")  # Or whatever available version is desired.

To use the default edition once again during the runtime session set the value to None.

This is the best way to assure a specific chart behavior for production application releases; however, once set any new JavaScript edition features or fixes will not be available until the code is removed or a different version is set.

Similarly, a custom URL for the JavaScript or CSS libraries can be set as well (for example, to facilitate development of CanvasXpress JS).

from canvasxpress.canvas import CanvasXpress

CanvasXpress.set_js_library_url("http://localhost:8080/js")
CanvasXpress.set_css_library_url("http://localhost:8080/css")

Customizing Charts

Generally speaking, a CanvasXpress object accepts the following parameters:

render_to

render_to is a str value that identifies the chart when rendered into HTML. JavaScript functions can use this ID to access the chart and perform CanvasXpress operations within the browser. Omitting render_to or setting it to None will make the CanvasXpress object assume an anonymous mode in which a new GUID will be generated each time graph() is called. If the chart will not be maniluated using JavaScript in the browser it is fine for charts to be anonymous.

NOTE: React environments regularly destroy and rebuild objects as the page is updated. In these environments it is possible for the timing of object destruction and JavaScript execution to cause a crash. The best defense is to either use anonymous mode, or if an ID must be known then a unique identifier should be set each time graph() is called. In this manner an ID for a chart in the middle of being recreated is never referenced. For example:

chart = CanvasXpress(...)
chart.render_to = str(guid4()).replace("-", "_")
return graph(chart)

Plotly's Dash framework uses React, and Dash applications should consider using only anonymous charts or assigning unique values as the ID similar to the above code. Shiny for Python does not seem to suffer from this challenge.

data

data sets the chart's data and metadata. This is an involved topic, and the introductory article is an excellent read to understand how data should be shaped. In general, data will be a dict (also known as an XYZ object), Web URL, or str.

Data dict example:

data_for_use_in_chart = {
    "y": {
        "data": [
            [random() % 100 for i in range(20)]
        ],
        "vars": ["A"],
    }
}

CanvasXpress for Python supports Pandas DataFrame assignments to data, plus supporting sample_annotation and variable_annotation properties. If data is assigned in this manner, then on generation of the JavaScript the CanvasXpress object will create an XYZ object using the DataFrame(s).

from canvasxpress.canvas import CanvasXpress
import pandas
import io
import requests

data_url = "https://www.canvasxpress.org/data/cX-generic-dat.txt"
data_raw = requests.get(data_url).content
data_df = pandas.read_csv(
    io.StringIO(data_raw.decode('utf-8')),
    sep="	",
    index_col=0,
)

sample_annot_url = "https://www.canvasxpress.org/data/cX-generic-smp.txt"
sample_annot_raw = requests.get(sample_annot_url).content
sample_annot_df = pandas.read_csv(
    io.StringIO(sample_annot_raw.decode('utf-8')),
    sep="	",
    index_col=0,
)

variable_annot_url = "https://www.canvasxpress.org/data/cX-generic-var.txt"
variable_annot_raw = requests.get(variable_annot_url).content
variable_annot_df = pandas.read_csv(
    io.StringIO(variable_annot_raw.decode('utf-8')),
    sep="	",
    index_col=0,
)

cx = CanvasXpress(
    data=data_df,
    sample_annotation=sample_annot_df,
    variable_annotation=variable_annot_df,
    config={
        "graphOrientation": "vertical",
        "graphType": "Dotplot",
        "lineType": "spline",
        "llmHeader": [
            ["V1", "V2", "V3", "V4", "Factor1", "Factor2", "Factor3", "Factor4", "Factor5", "Factor6"]
        ],
        "showSmpOverlaysLegend": True,
        "smpOverlayProperties": {
            "Factor4": {
                "color": "blue",
                "thickness": 50,
                "type": "Bar",
                "showLegend": "True"
            },
            "Factor5": {
                "thickness": 50,
                "color": "grey",
                "type": "Bar",
                "showLegend": "True"
            },
            "Factor6": {
                "showLegend": "True",
                "thickness": 50,
                "color": "red",
                "type": "Bar"
            },
            "Factor1": {
                "type": "Default",
                "color": "rgb(10,176,219)",
                "spectrum": ["rgb(69,117,180)", "rgb(145,191,219)", "rgb(224,243,248)", "rgb(255,255,191)",
                             "rgb(254,224,144)", "rgb(252,141,89)", "rgb(215,48,39)"],
                "scheme": "CanvasXpress",
                "hideName": False,
                "hideValue": False,
                "showLegend": True,
                "legendColumns": False,
                "showBox": True,
                "ticksOnBottomOrLeft": True,
                "rotate": False,
                "invert": False,
                "position": "bottom"
            },
            "Factor2": {
                "type": "Default",
                "color": "rgb(254,211,133)",
                "spectrum": ["rgb(69,117,180)", "rgb(145,191,219)", "rgb(224,243,248)", "rgb(255,255,191)",
                             "rgb(254,224,144)", "rgb(252,141,89)", "rgb(215,48,39)"],
                "scheme": "CanvasXpress",
                "hideName": False,
                "hideValue": False,
                "showLegend": True,
                "legendColumns": False,
                "showBox": True,
                "ticksOnBottomOrLeft": True,
                "rotate": False,
                "invert": False,
                "position": "bottom"
            },
            "Factor3": {
                "type": "Default",
                "color": "rgb(254,105,105)",
                "spectrum": ["rgb(69,117,180)", "rgb(145,191,219)", "rgb(224,243,248)", "rgb(255,255,191)",
                             "rgb(254,224,144)", "rgb(252,141,89)", "rgb(215,48,39)"],
                "scheme": "CanvasXpress",
                "hideName": False,
                "hideValue": False,
                "showLegend": True,
                "legendColumns": False,
                "showBox": True,
                "ticksOnBottomOrLeft": True,
                "rotate": False,
                "invert": False,
                "position": "bottom"
            }
        },
        "smpOverlays": ["Factor1", "Factor2", "Factor3"],
        "smpTextRotate": 45,
        "smpTitle": "Collection of Samples",
        "smpTitleFontStyle": "italic",
        "subtitle": "Random Data",
        "theme": "CanvasXpress",
        "title": "Dotplot Graph",
        "xAxis": ["V1", "V2", "V3", "V4"],
        "xAxisTickFormat": "%.0f Mil."
    },
)

If a DataFrame is assigned to data then its index will be used for xyz["y"]["vars"] values and its header will be used for the xyz["y"]["smps"] values.

If a DataFrame is assigned to sample_annotation or variable_annotation then the following strategy will be used to determine how the DataFrame should be parsed to create the corresponding x and z properties, respectively:

1. The first column is first inspected to see if all of the column values match one of the available sample (xyz["y"]["smps"] aka columns) or variable (xyz["y"]["vars"] aka rows) values.
2. If a match is not made within the column, then the first row is inspected for the same criteria.
3. Next, the DataFrame headers will be inspected.
4. Finally, the DataFrame index will be used regardless of a match.

If no DataFrame is assigned to the sample_annotation or variable_annotation properties then those portions of the xyz object will simply be ommitted.

sample_annotation and variable_annotation can only be used if the data property is already a DataFrame. If any other type is used, such as a dict or str then an exception will be raised.

data, sample_annotation, and variable_annotation can be set to None to remove their values.

Data URL example:

data_for_use_in_chart = "https://corgis-edu.github.io/corgis/datasets/csv/state_demographics/state_demographics.csv"

Data text (CSV) example:

data_for_use_in_chart = """
"State","Population.Population Percent Change","Population.2014 Population"
"Connecticut","-10.2","3605944"
"Delaware","8.4","989948"
"""

config

config describes the chart's formatting. It is a dict in which properties are specified and assigned values. All of the values must be compliant with Python's json.dumps() function. For example:

config = {
             "background": "rgb(255,255,255)",
             "colorScheme": "CanvasXpress",
             "graphOrientation": "vertical",
             "graphType": "Area",
             "objectBorderColor": False,
             "plotBox": False,
             "plotBoxColor": "rgb(204,204,204)",
             "showLegend": False,
             "showLegendBorder": True,
             "smpLabelRotate": 90,
             "smpTitle": "time",
             "xAxis": ["A"],
             "xAxisTickRightShow": False,
             "yAxisTickTopShow": False
         },

Configuration options may also be specified as keyword arguments in the CanvasXpress function call. For example:

CanvasXpress(
    data={
        "y": {
            "vars": ["Gene1"],
            "smps": ["Smp1", "Smp2", "Smp3"],
            "data": [[10, 35, 88]]
        }
    },
    graphOrientation="vertical",
    graphType="Bar",
    showLegend=False,
    smpLabelRotate=90,
    smpTitle="Samples",
    theme="CanvasXpress",
    title="Bar Graph Title",
    xAxisTitle="Value"
)

If config and configuration keyword arguments are specified together, their configuration options are combined, with the keyword arguments overriding any item of the same name in config. This approach can be used to define a generic configuration and allow for ad hoc modifications.

width and height

width and height specify the chart's dimensions as pixels. If ommitted the CanvasXpress edition active for the browser will assign default values, such as 500px by 500px.

Javascript Events

CanvasXpress provides support for Javascript events via hook functions that are called when events occur, such as mouse movement or clicks. These events are supported via the canvasxpress.js sub-package. CXEvent objects hold the Javascript instructions for Web events. An example event for graph clicks with popup information is:

from canvasxpress.js.function import CXEvent

CXEvent(
    id="click",
    script="""
    var s = 'click on var ' + o.y.vars[0] + ' and smp ' + o.y.smps[0];
    t.showInfoSpan(e, s);
    """
)

The general JavaScript template of a CanvasXpress Javascript hook function is:

function (o, e, t) {
    // script logic goes here
};

CXEvent objects can be provided as a single object or as a list. Here's an example of an event the provides additional information about chart data upon a user click:

from canvasxpress.canvas import CanvasXpress
from canvasxpress.plot import graph
from canvasxpress.js.function import CXEvent

graph(
    CanvasXpress(
        render_to="example_chart",
        data={
            "y": {
                "vars": ["Gene1"],
                "smps": ["Smp1", "Smp2", "Smp3"],
                "data": [[10, 35, 88]]
            }
        },
        config={
            "graphOrientation": "vertical",
            "graphType": "Bar",
            "showLegend": False,
            "smpLabelRotate": 90,
            "smpTitle": "Samples",
            "theme": "CanvasXpress",
            "title": "Bar Graph Title",
            "xAxisTitle": "Value"
        },
        events=[
            CXEvent(
                id="click",
                script="""
                var s = 'click on var ' + o.y.vars[0] + ' and smp ' + o.y.smps[0];
                t.showInfoSpan(e, s);
                """
            ),
        ]
    )
)

Converting to and from Reproducible JSON

CanvasXpress for Python can also convert to and from reproducible JSONs usable with the JavaScript and R editions of the library. convert_to_reproducible_json takes an existing CanvasXpress object and provides a str copy of the JSON, which can then be logged for debugging or saved to disk for use elsewhere. convert_from_reproducible_json does the opposite by taking a reproducible JSON str and providing the CanvasXpress object equivalent.

Note: Events are not currently supported for import. This will be provided in a future edition. Export supports events.

For example, do the following to see the JSON in the Python console:

from canvasxpress.canvas import CanvasXpress
from canvasxpress.plot import convert_to_reproducible_json
from canvasxpress.js.function import CXEvent

print(
    convert_to_reproducible_json(
        CanvasXpress(
            render_to="example_chart",
            data={
                "y": {
                    "vars": ["Gene1"],
                    "smps": ["Smp1", "Smp2", "Smp3"],
                    "data": [[10, 35, 88]]
                }
            },
            config={
                "graphOrientation": "vertical",
                "graphType": "Bar",
                "showLegend": False,
                "smpLabelRotate": 90,
                "smpTitle": "Samples",
                "theme": "CanvasXpress",
                "title": "Bar Graph Title",
                "xAxisTitle": "Value"
            },
            events=[
                CXEvent(
                    id="click",
                    script="""
                    var s = 'click on var ' + o.y.vars[0] + ' and smp ' + o.y.smps[0];
                    t.showInfoSpan(e, s);
                    """
                ),
            ]
        )
    )
)

The console would display:

{
    "renderTo": "example_chart",
    "data": {"y": {"vars": ["Gene1"], "smps": ["Smp1", "Smp2", "Smp3"], "data": [[10, 35, 88]]}, "x": {}, "z": {}},
    "config": {"graphOrientation": "vertical", "graphType": "Bar", "showLegend": false, "smpLabelRotate": 90, "smpTitle": "Samples", "theme": "CanvasXpress", "title": "Bar Graph Title", "xAxisTitle": "Value"},
    "afterRender": [],
    "otherParams": {},
    "events": {'click': function(o, e, t){
                    var s = 'click on var ' + o.y.vars[0] + ' and smp ' + o.y.smps[0];
                    t.showInfoSpan(e, s);
                    }},
    "width": 500,
    "height": 500
}

This text could be saved to a file, such as example.json, and then dragged onto a CanvasXpress chart in a browser to load the equivalent chart. In fact, CanvasXpress for Python uses the core functionality producing JSON output to make charts available in contexts such as Dash and Shiny.

from canvasxpress.canvas import CanvasXpress
from canvasxpress.plot import show_in_browser

if __name__ == "__main__":
    # Define a CX bar chart with some basic data
    chart: CanvasXpress = CanvasXpress(
        data={
            "y": {
                "vars": ["Gene1"],
                "smps": ["Smp1", "Smp2", "Smp3"],
                "data": [[10, 35, 88]]
            }
        },
        config={
            "graphType": "Bar"
        }
    )

    # Display the chart in its own Web page
    show_in_browser(chart)

Upon running the example the following chart will be displayed on systems such as MacOS X, Windows, and Linux with graphical systems:

A basic Shiny for Python app provides a means by which:

1. A local development server can be started
2. A function can respond to input or draw an initial UI

First install Shiny for Python and CanvasXpress for Python:

pip install shiny
pip install canvasxpress[shiny]

Then create a demo file, such as app.py, and insert:

from random import random

from shiny import App, ui, render, reactive

from canvasxpress.canvas import CanvasXpress
from canvasxpress.render.shiny import output_canvasxpress
from canvasxpress.plot import graph

app_ui = ui.page_fluid(
    ui.row(
        ui.input_slider(
            "points_desired",
            "Points",
            min=0,
            max=100,
            value=0,
        ),
    ),
    ui.row(
        output_canvasxpress("chart_view"),
    )
)


def server(input, output, session):
    @render.ui
    @reactive.event(input.points_desired)
    def chart_view():
        return graph(
            CanvasXpress(
                data={
                    "y": {
                        "data": [
                            [random() % 100 for i in range(input.points_desired())]
                        ],
                        "vars": ["A"],
                    }
                },
                config={
                    "background": "rgb(255,255,255)",
                    "colorScheme": "CanvasXpress",
                    "graphOrientation": "vertical",
                    "graphType": "Area",
                    "objectBorderColor": False,
                    "plotBox": False,
                    "plotBoxColor": "rgb(204,204,204)",
                    "showLegend": False,
                    "showLegendBorder": True,
                    "smpLabelRotate": 90,
                    "smpTitle": "time",
                    "xAxis": ["A"],
                    "xAxisTickRightShow": False,
                    "yAxisTickTopShow": False
                },
                width=500,
                height=500
            )
        )


app = App(app_ui, server)

Run the App and View the Page

On the command line, execute:

shiny run --reload --launch-browser app.py

And output similar to the following will be provided:

Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Browsing to http://localhost:8000/ will result in a page with a CanvasXpress chart, which is being hosted by the Shiny for Python framework:

Congratulations! You have created a Shiny for Python CanvasXpress app!

A basic Streamlit app provides a means by which:

1. A local development server can be started
2. A function can respond to a URL

First install Streamlit and CanvasXpress for Python:

pip install streamlit
pip install canvasxpress[streamlit]

Then create a demo file, such as app.py, and insert:

import random

import streamlit as st

from canvasxpress.canvas import CanvasXpress
from canvasxpress.plot import graph

# A basic bar chart.  It's anonymous, so no render_to.  Data is added during the draw phase.
bar_chart = CanvasXpress(
    config={
        "graphOrientation": "vertical",
        "plotBox": True,
        "showLegend": False,
        "smpLabelRotate": 90,
        "smpTitle": "Samples",
        "theme": "CanvasXpress",
        "title": "Bar Graph Title",
        "xAxis": ["V1"],
        "xAxisTitle": "Value",
        "graphType": "Bar"
    },
    width=500,
    height=500
)

# Write the UI to the browser
# This code will be re-executed with each click of the button

# Name the theme
st.title('CanvasXpress in Streamlit!')

# Some columns to organize the button and chart
column1, column2 = st.columns([1, 3])

# A column with our data generator button
with column1:
    # This has no associated action, so by default it triggers a redraw of the UI.
    st.button("Generate New Data")

# Another column with the chart displayed
# With each redraw generate new random values
bar_chart.data = {
    "y": {
        "vars": ["V1"],
        "smps": ["S1", "S2", "S3"],
        "data": [
            [
                random.randint(100, 10000),
                random.randint(100, 10000),
                random.randint(100, 10000),
            ]
        ]
    }
}
with column2:
    # This plots the CanvasXpress chart into the UI.
    graph(bar_chart)

Run the App and View the Page

On the command line, execute:

streamlit run app.py

And output similar to the following will be provided:

Running on http://localhost:8501/ (Press CTRL+C to quit)

Browsing to http://localhost:8501/ will result in a page with a CanvasXpress chart, which is being hosted by the Streamlit framework:

Congratulations! You have created a Streamlit CanvasXpress app!

Create a Basic Dash App

A basic Dash app provides a means by which:

1. A local development server can be started
2. A function can respond to a URL

First install Dash and CanvasXpress for Python:

pip install dash
pip install canvasxpress[dash]

Then create a demo file, such as app.py, and insert:

from random import random

from dash import Dash, html

from canvasxpress.canvas import CanvasXpress
from canvasxpress.plot import graph

g_app = Dash(__name__)

colors = {
    "background": "#111111",
    "text": "rgb(127,219,255)",
}

# Application
g_app.layout = html.Div(
    style={"backgroundColor": colors["background"]},
    children=[
        html.H1(
            children="Hello Dash",
            style={"textAlign": "center", "color": colors["text"]},
        ),
        html.H2(
            children=(
                "An Example of CanvasXpress Chart in Plotly Dash"
            ),
            style={"textAlign": "center", "color": colors["text"]},
        ),
        html.Div(
            id="chart-container",
            children=[
                html.Div(
                    id="cx-container",
                    style={"textAlign": "center"},
                    children=graph(
                        CanvasXpress(
                            data={
                                "y": {
                                    "data": [
                                        [random() % 100 for i in range(5)]
                                    ],
                                    "vars": ["A"],
                                }
                            },
                            config={
                                "background": "rgb(255,255,255)",
                                "colorScheme": "CanvasXpress",
                                "graphOrientation": "vertical",
                                "graphType": "Area",
                                "objectBorderColor": False,
                                "plotBox": False,
                                "plotBoxColor": "rgb(204,204,204)",
                                "showLegend": False,
                                "showLegendBorder": True,
                                "smpLabelRotate": 90,
                                "smpTitle": "time",
                                "xAxis": ["A"],
                                "xAxisTickRightShow": False,
                                "yAxisTickTopShow": False
                            },
                            width=500,
                            height=500
                        )
                    ),
                ),
            ],
        ),
    ],
)

if __name__ == "__main__":
    g_app.run_server(debug=True)

Run the App and View the Page

On the command line, execute:

python3 app.py

And output similar to the following will be provided:

Running on http://127.0.0.1:8050/ (Press CTRL+C to quit)

Browsing to http://127.0.0.1:8050/ will result in a page with a CanvasXpress chart, which is being hosted by the Dash framework:

Congratulations! You have created a Plotly Dash CanvasXpress app!

Create a Basic Flask App

A basic Flask app provides a means by which:

1. A local development server can be started
2. A function can respond to a URL

First install Flask and CanvasXpress for Python:

pip install -U Flask canvasxpress

Then create a demo file, such as app.py, and insert:

# save this as app.py
from flask import Flask

app = Flask(__name__)


@app.route('/')
def canvasxpress_example():
    return "Hello!"

On the command line, execute:

flask run

And output similar to the following will be provided:

Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Browsing to http://127.0.0.1:5000/ will result in a page with the text Hello!.

Add a Chart

CanvasXpress for Python can be used to define a chart with various attributes and then generate the necessary HTML and Javascript for proper display in the browser.

Add a templates directory to the same location as the app.py file, and inside add a file called canvasxpress_example.html. Inside the file add:

<html>
<head>
    <meta charset="UTF-8">
    <title>Flask CanvasXpress Example</title>

    <!-- 2. Include the CanvasXpress library -->
    <link
            href='https://www.canvasxpress.org/dist/canvasXpress.css'
            rel='stylesheet'
            type='text/css'
    />
    <script
            src='https://www.canvasxpress.org/dist/canvasXpress.min.js'
            type='text/javascript'>
    </script>

    <!-- 3. Include script to initialize object -->
    <script type="text/javascript">
        onReady(function () {
            {
                {
                    canvas_source | safe
                }
            }
        })
    </script>

</head>
<body>

<!-- 1. DOM element where the visualization will be displayed -->
{{canvas_element|safe}}

</body>
</html>

The HTML file, which uses Jinja syntax achieves three things:

1. Provides a location for a <div> element that marks where the chart will be placed.
2. References the CanvasXpress CSS and JS files needed to illustrate and operate the charts.
3. Provides a location for the Javascript that will replace the chart <div> with a working element on page load.

Going back to our Flask app, we can add a basic chart definition with some data to our example function:

from flask import Flask, render_template
from canvasxpress.canvas import CanvasXpress

app = Flask(__name__)


@app.route('/')
def canvasxpress_example():
    # Define a CX bar chart with some basic data
    chart: CanvasXpress = CanvasXpress(
        data={
            "y": {
                "vars": ["Gene1"],
                "smps": ["Smp1", "Smp2", "Smp3"],
                "data": [[10, 35, 88]]
            }
        },
        config={
            "graphType": "Bar"
        }
    )

    # Get the HTML parts for use in our Web page:
    html_parts: dict = chart.render_to_html_parts()

    # Return a Web page based on canvasxpress_example.html and our HTML parts
    return render_template(
        "canvasxpress_example.html",
        canvas_element=html_parts["cx_canvas"],
        canvas_source=html_parts["cx_js"]
    )

Run the App and View the Page

Rerun the flask app on the command line and browse to the indicated IP and URL. A page similar to the following will be displayed:

Congratulations! You have created a Flask CanvasXpress app!