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Sample code for the article on Altair #754

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Sample code for the article on Altair
lpozo Apr 9, 2026
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3 changes: 3 additions & 0 deletions altair-python/README.md
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# Altair: Declarative Charts With Python

This folder provides the code examples for the Real Python tutorial [Altair: Declarative Charts With Python](https://realpython.com/altair-python/).
732 changes: 732 additions & 0 deletions altair-python/altair-python.ipynb
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20 changes: 20 additions & 0 deletions altair-python/scatter_basic.py
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import altair as alt
from altair.datasets import data

movies = data.movies()
movies = movies.dropna(
subset=[
"Production Budget",
"Worldwide Gross",
]
)

scatter = (
alt.Chart(movies)
.mark_point()
.encode(
x="Production Budget:Q",
y="Worldwide Gross:Q",
)
)
scatter
43 changes: 43 additions & 0 deletions altair-python/scatter_connected.py
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import altair as alt
from altair.datasets import data

movies = data.movies()
movies = movies.dropna(
subset=[
"Production Budget",
"Worldwide Gross",
"IMDB Rating",
"Major Genre",
]
)

brush = alt.selection_interval()

scatter = (
alt.Chart(movies)
.mark_point()
.encode(
x="Production Budget:Q",
y="Worldwide Gross:Q",
color=(
alt.when(brush)
.then("Major Genre:N")
.otherwise(alt.value("lightgray")),
),
Comment on lines +22 to +26
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Copilot AI Apr 9, 2026

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The extra parentheses around the color= expression are unnecessary and make this already-long line harder to read. Consider removing the redundant parentheses and letting the formatter wrap the chained call for readability.

Suggested change
color=(
alt.when(brush)
.then("Major Genre:N")
.otherwise(alt.value("lightgray")),
),
color=alt.when(brush)
.then("Major Genre:N")
.otherwise(alt.value("lightgray")),

Copilot uses AI. Check for mistakes.
)
.add_params(brush)
)

scatter

bars = (
alt.Chart(movies)
.mark_bar()
.encode(
x="mean(IMDB Rating):Q",
y="Major Genre:N",
)
.transform_filter(brush)
)

scatter & bars
25 changes: 25 additions & 0 deletions altair-python/scatter_encoding_channels.py
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import altair as alt
from altair.datasets import data
Comment on lines +1 to +2
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Copilot AI Apr 9, 2026

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The filename contains a space and the suffix "copy", which makes it awkward to import/execute from shells and looks like an accidental duplicate. Please rename this file to a conventional slug/snake-case name without spaces (and without "copy"), e.g. "scatter_encoding_channels.py".

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movies = data.movies()
movies = movies.dropna(
subset=[
"Production Budget",
"Worldwide Gross",
"IMDB Rating",
"Major Genre",
]
)

scatter = (
alt.Chart(movies)
.mark_point()
.encode(
x="Production Budget:Q",
y="Worldwide Gross:Q",
color="Major Genre:N",
size="IMDB Rating:Q",
tooltip=["Title:N", "IMDB Rating:Q"],
)
)
scatter
27 changes: 27 additions & 0 deletions altair-python/scatter_faceted.py
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@@ -0,0 +1,27 @@
import altair as alt
from altair.datasets import data

movies = data.movies()
movies = movies.dropna(
subset=[
"Production Budget",
"Worldwide Gross",
"IMDB Rating",
"Major Genre",
"MPAA Rating",
]
)

scatter = (
alt.Chart(movies)
.mark_point()
.encode(
x="Production Budget:Q",
y="Worldwide Gross:Q",
color="Major Genre:N",
size="IMDB Rating:Q",
tooltip=["Title:N", "IMDB Rating:Q"],
column="MPAA Rating:O",
)
)
scatter
19 changes: 19 additions & 0 deletions altair-python/steps.py
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@@ -0,0 +1,19 @@
import altair as alt
import pandas as pd

steps = pd.DataFrame(
{
"Day": ["1-Mon", "2-Tue", "3-Wed", "4-Thu", "5-Fri", "6-Sat", "7-Sun"],
"Steps": [6200, 8400, 7100, 9800, 5500, 9870, 3769],
}
)

weekly_steps = (
alt.Chart(steps)
.mark_bar()
.encode(
x="Day",
y="Steps",
Comment on lines +15 to +16
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Copilot AI Apr 9, 2026

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Unlike the other examples in this folder, the encodings here don’t specify field types (e.g. Day:N, Steps:Q). Making the types explicit keeps the example consistent and avoids relying on Altair’s type inference if the data source changes.

Suggested change
x="Day",
y="Steps",
x="Day:N",
y="Steps:Q",

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)
)
weekly_steps
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