docs.sheetjs.com/docz/docs/03-demos/01-math/21-pandas.md

---
title: Spreadsheet Data in Python
sidebar_label: Python DataFrames
description: Process structured data in Python DataFrames. Seamlessly integrate spreadsheets into your workflow with SheetJS. Analyze complex Excel spreadsheets with confidence.
pagination_prev: demos/index
pagination_next: demos/frontend/index
---

import current from '/version.js';
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import CodeBlock from '@theme/CodeBlock';

[Pandas](https://pandas.pydata.org/) is a Python library for data analysis.

[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.

This demo uses SheetJS to process data from a spreadsheet and translate to the
Pandas DataFrame format. We'll explore how to load SheetJS from Python scripts,
generate DataFrames from workbooks, and write DataFrames back to workbooks.

The ["Complete Example"](#complete-example) includes a wrapper library that
simplifies importing and exporting spreadsheets.

:::info pass

Pandas includes limited support for reading spreadsheets (`pandas.from_excel`)
and writing XLSX spreadsheets (`pandas.DataFrame.to_excel`).

**SheetJS supports many common spreadsheet formats that Pandas cannot process.**

SheetJS operations also offer more flexibility in processing complex worksheets.

:::

:::note Tested Environments

This demo was tested in the following deployments:

| Architecture | JS Engine       | Pandas | Python | Date       |
|:-------------|:----------------|:-------|:-------|:-----------|
| `darwin-x64` | Duktape `2.7.0` | 2.2.1  | 3.12.2 | 2024-03-15 |
| `darwin-arm` | Duktape `2.7.0` | 2.0.3  | 3.11.7 | 2024-02-13 |
| `linux-x64`  | Duktape `2.7.0` | 1.5.3  | 3.11.3 | 2024-01-29 |

:::

## Integration Details

[`sheetjs.py`](pathname:///pandas/sheetjs.py) is a wrapper script that provides
helper methods for reading and writing spreadsheets. Installation notes are
included in the ["Complete Example"](#complete-example) section.

### JS in Python

JS code cannot be directly evaluated in Python implementations.

To run JS code from Python, JavaScript engines[^1] can be embedded in Python
modules or dynamically loaded using the `ctypes` foreign function library[^2].
This demo uses `ctypes` with the [Duktape engine](/docs/demos/engines/duktape).

### Wrapper

The script exports a class named `SheetJSWrapper`. It is a context manager that
initializes the Duktape engine and executes SheetJS scripts on entrance. All
work should be performed in the context:

```python title="Complete Example"
#!/usr/bin/env python3
from sheetjs import SheetJSWrapper

with SheetJSWrapper() as sheetjs:

  # Parse file
  wb = sheetjs.read_file("pres.numbers")
  print("Loaded file pres.numbers")

  # Get first worksheet name
  first_ws_name = wb.get_sheet_names()[0]
  print(f"Reading from sheet {first_ws_name}")

  # Generate DataFrame from first worksheet
  df = wb.get_df(first_ws_name)
  print(df.info())

  # Export DataFrame to XLSB
  sheetjs.write_df(df, "SheetJSPandas.xlsb", sheet_name="DataFrame")
```

### Reading Files

`sheetjs.read_file` accepts a path to a spreadsheet file. It will parse the file
and return an object representing the workbook.

The `get_sheet_names` method of the workbook returns a list of sheet names.

The `get_df` method of the workbook generates a DataFrame from the workbook. The
specific sheet can be selected by passing the name.

For example, the following code reads `pres.numbers` and generates a DataFrame
from the second worksheet:

```python title="Generating a DataFrame from the second worksheet"
with SheetJSWrapper() as sheetjs:
  # Parse file
  wb = sheetjs.read_file(path)

  # Generate DataFrame from second worksheet
  ws_name = wb.get_sheet_names()[1]
  df = wb.get_df(ws_name)

  # Print metadata
  print(df.info())
```

Under the hood, `sheetjs.py` performs the following steps:

```mermaid
flowchart LR
  file[(workbook\nfile)]
  subgraph SheetJS operations
    bytes(Byte\nstring)
    wb((SheetJS\nWorkbook))
    csv(CSV\nstring)
  end
  subgraph Pandas operations
    stream(CSV\nStream)
    df[(Pandas\nDataFrame)]
  end
  file --> |`open`/`read`\nPython ops| bytes
  bytes --> |`XLSX.read`\nParse Bytes| wb
  wb --> |`sheet_to_csv`\nExtract Data| csv
  csv --> |`StringIO`\nPython ops| stream
  stream --> |`read_csv`\nParse CSV| df
```

1) Pure Python operations read the spreadsheet file and generate a byte string.

2) SheetJS libraries parse the string and generate a clean CSV.

- The `read` method[^3] parses file bytes into a SheetJS workbook object[^4]
- After selecting a worksheet, `sheet_to_csv`[^5] generates a CSV string

3) Python operations convert the CSV string to a stream object.[^6]

4) The Pandas `read_csv` method[^7] ingests the stream and generate a DataFrame.

### Writing Files

`sheetjs.write_df` accepts a DataFrame and a path. It will attempt to export
the data to a spreadsheet file.

For example, the following code exports a DataFrame to `SheetJSPandas.xlsb`:

```python title="Exporting a DataFrame to XLSB"
with SheetJSWrapper() as sheetjs:
  # Export DataFrame to XLSB
  sheetjs.write_df(df, "SheetJSPandas.xlsb", sheet_name="DataFrame")
```

Under the hood, `sheetjs.py` performs the following steps:

```mermaid
flowchart LR
  subgraph Pandas operations
    df[(Pandas\nDataFrame)]
    json(JSON\nString)
  end
  subgraph SheetJS operations
    aoo(array of\nobjects)
    wb((SheetJS\nWorkbook))
    u8a(File\nbytes)
  end
  file[(workbook\nfile)]
  df --> |`to_json`\nPandas ops| json
  json --> |`JSON.parse`\nJS Engine| aoo
  aoo --> |`json_to_sheet`\nSheetJS Ops| wb
  wb --> |`XLSX.write`\nUint8Array| u8a
  u8a --> |`open`/`write`\nPython ops| file
```

1) The Pandas DataFrame `to_json` method[^8] generates a JSON string.

2) JS engine operations translate the JSON string to an array of objects.

3) SheetJS libraries process the data array and generate file bytes.

- The `json_to_sheet` method[^9] creates a SheetJS sheet object from the data.
- The `book_new` method[^10] creates a SheetJS workbook that includes the sheet.
- The `write` method[^11] generates the spreadsheet file bytes.

4) Pure Python operations write the bytes to file.

## Complete Example

This example will extract data from an Apple Numbers spreadsheet and generate a
DataFrame. The DataFrame will be exported to the binary XLSB spreadsheet format.

0) Install Pandas:

```bash
sudo python3 -m pip install pandas
```

:::caution pass

On Arch Linux-based platforms including the Steam Deck, the install may fail:

```
error: externally-managed-environment
```

In these situations, Pandas must be installed through the package manager:

```bash
sudo pacman -Syu python-pandas
```

:::

:::caution pass

On macOS systems with a Python version from Homebrew, the install will fail:

```
error: externally-managed-environment
```

When the demo was last tested, Homebrew did not have a pre-built Pandas formula.
Instead, Pandas should be installed with the `--break-system-packages` option:

```bash
sudo python3 -m pip install pandas --break-system-packages
```

:::

1) Build the Duktape shared library:

```bash
curl -LO https://duktape.org/duktape-2.7.0.tar.xz
tar -xJf duktape-2.7.0.tar.xz
cd duktape-2.7.0
make -f Makefile.sharedlibrary
cd ..
```

2) Copy the shared library to the current folder. When the demo was last tested,
the shared library file name differed by platform:

| OS     | name                      |
|:-------|:--------------------------|
| Darwin | `libduktape.207.20700.so` |
| Linux  | `libduktape.so.207.20700` |

```bash
cp duktape-*/libduktape.* .
```

3) Download the SheetJS Standalone script and move to the project directory:

<ul>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js`}>shim.min.js</a></li>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}>xlsx.full.min.js</a></li>
</ul>

<CodeBlock language="bash">{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}
</CodeBlock>

4) Download the following test scripts and files:

- [`pres.numbers` test file](https://sheetjs.com/pres.numbers)
- [`sheetjs.py` script](pathname:///pandas/sheetjs.py)
- [`SheetJSPandas.py` script](pathname:///pandas/SheetJSPandas.py)

```bash
curl -LO https://sheetjs.com/pres.numbers
curl -LO https://docs.sheetjs.com/pandas/sheetjs.py
curl -LO https://docs.sheetjs.com/pandas/SheetJSPandas.py
```

5) Edit the `sheetjs.py` script.

The `lib` variable declares the path to the library:

```python title="sheetjs.py (edit highlighted line)"
# highlight-next-line
lib = "libduktape.207.20700.so"
```

<Tabs groupId="triple">
  <TabItem value="darwin-x64" label="MacOS">

The name of the library is `libduktape.207.20700.so`:

```python title="sheetjs.py (change highlighted line)"
# highlight-next-line
lib = "libduktape.207.20700.so"
```

  </TabItem>
  <TabItem value="linux-x64" label="Linux">

The name of the library is `libduktape.so.207.20700`:

```python title="sheetjs.py (change highlighted line)"
# highlight-next-line
lib = "libduktape.so.207.20700"
```

  </TabItem>
</Tabs>

6) Run the script:

```bash
python3 SheetJSPandas.py pres.numbers
```

If successful, the script will display DataFrame metadata:

```
RangeIndex: 5 entries, 0 to 4
Data columns (total 2 columns):
 #   Column  Non-Null Count  Dtype
---  ------  --------------  -----
 0   Name    5 non-null      object
 1   Index   5 non-null      int64
dtypes: int64(1), object(1)
```

It will also export the DataFrame to `SheetJSPandas.xlsb`. The file can be
inspected with a spreadsheet editor that supports XLSB files.

## Other Libraries

Other Python DataFrame libraries mirror the Pandas DataFrame API.

### Polars

[Polars](https://pola.rs/) is a similar DataFrame library that offers many
features from Pandas DataFrames.

:::info pass

Polars includes limited support for reading and writing spreadsheets by wrapping
third-party libraries. In practice, Polars communicates with the third-party
libraries using intermediate CSV files.[^12]

**SheetJS supports many common spreadsheet formats that Polars cannot process.**

SheetJS operations also offer more flexibility in processing complex worksheets.

:::

The Pandas example requires a few slight changes to work with Polars:

- Polars DataFrames expose `write_json` instead of `to_json`:

```diff
-  json = df.to_json(orient="records")
+  json = df.write_json(row_oriented=True)
```

- Polars DataFrames do not expose `info`

#### Polars Demo

:::note Tested Environments

This demo was tested in the following deployments:

| Architecture | JS Engine       | Polars  | Python | Date       |
|:-------------|:----------------|:--------|:-------|:-----------|
| `darwin-x64` | Duktape `2.7.0` | 0.20.15 | 3.12.2 | 2024-03-15 |
| `darwin-arm` | Duktape `2.7.0` | 0.20.7  | 3.11.7 | 2024-02-13 |
| `linux-x64`  | Duktape `2.7.0` | 0.20.6  | 3.11.3 | 2024-01-30 |

:::

0) Follow the [Pandas "Complete Example"](#complete-example) through the end.

1) Edit `sheetjs.py`.

Near the top of the script, change the import from `pandas` to `polars`:

```diff title="sheetjs.py (apply changes)"
-from pandas import read_csv
+from polars import read_csv
```

:::note pass

The red lines starting with `-` should be removed from the file and the green
lines starting with `+` should be added to the file. Black lines show the source
context and should not be changed.

:::

Within the `export_df_to_wb` function, change the `df.to_json` line:

```diff title="sheetjs.py (apply changes)"
 def export_df_to_wb(ctx, df, path, sheet_name="Sheet1", book_type=None):
-  json = df.to_json(orient="records")
+  json = df.write_json(row_oriented=True)
```

2) Edit `SheetJSPandas.py`.

In the script, change `df.info()` to `df`:

```diff title="SheetJSPandas.py (apply changes)"
 def export_df_to_wb(ctx, df, path, sheet_name="Sheet1", book_type=None):
-    print(df.info())
+    print(df)
```

Change the export filename from `SheetJSPandas.xlsb` to `SheetJSPolars.xlsb`:

```diff
     # Export DataFrame to XLSB
-    sheetjs.write_df(df, "SheetJSPandas.xlsb", sheet_name="DataFrame")
+    sheetjs.write_df(df, "SheetJSPolars.xlsb", sheet_name="DataFrame")
```

3) Install Polars:

```bash
sudo python3 -m pip install polars
```

:::caution pass

On Arch Linux-based platforms including the Steam Deck, the install may fail:

```
error: externally-managed-environment
```

It is recommended to use a virtual environment for Polars:

```bash
mkdir sheetjs-polars
cd sheetjs-polars
python3 -m venv .
./bin/pip install polars
```

:::

4) Run the script:

```bash
python3 SheetJSPandas.py pres.numbers
```

:::note pass

If the virtual environment was configured in the previous step, run:

```bash
./bin/python3 SheetJSPandas.py pres.numbers
```

:::

If successful, the script will display DataFrame data:

```
shape: (5, 2)
┌──────────────┬───────┐
│ Name         ┆ Index │
│ ---          ┆ ---   │
│ str          ┆ i64   │
╞══════════════╪═══════╡
│ Bill Clinton ┆ 42    │
│ GeorgeW Bush ┆ 43    │
│ Barack Obama ┆ 44    │
│ Donald Trump ┆ 45    │
│ Joseph Biden ┆ 46    │
└──────────────┴───────┘
```

It will also export the DataFrame to `SheetJSPolars.xlsb`. The file can be
inspected with a spreadsheet editor that supports XLSB files.

[^1]: See ["Other Languages"](/docs/demos/engines/) for more examples.
[^2]: See [`ctypes`](https://docs.python.org/3/library/ctypes.html) in the Python documentation.
[^3]: See [`read` in "Reading Files"](/docs/api/parse-options)
[^4]: See ["Workbook Object"](/docs/csf/book)
[^5]: See [`sheet_to_csv` in "Utilities"](/docs/api/utilities/csv#delimiter-separated-output)
[^6]: See [the examples in "IO tools"](https://pandas.pydata.org/pandas-docs/stable/user_guide/io.html) in the Pandas documentation.
[^7]: See [`pandas.read_csv`](https://pandas.pydata.org/docs/reference/api/pandas.read_csv.html) in the Pandas documentation.
[^8]: See [`pandas.DataFrame.to_json`](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.to_json.html) in the Pandas documentation.
[^9]: See [`json_to_sheet` in "Utilities"](/docs/api/utilities/array#array-of-objects-input)
[^10]: See [`book_new` in "Utilities"](/docs/api/utilities/wb)
[^11]: See [`write` in "Writing Files"](/docs/api/write-options)
[^12]: As explained [in the Polars documentation](https://docs.pola.rs/py-polars/html/reference/api/polars.read_excel.html), "... the target Excel sheet is first converted to CSV ... and then parsed with Polars’ `read_csv()` function."