kosiew opened a new issue, #1171:
URL: https://github.com/apache/datafusion-python/issues/1171
## Description:
Currently, DataFrameHtmlFormatter tracks a _styles_loaded class flag in
Python to avoid re-injecting styles and scripts across notebook cells. However,
this approach:
- Doesn’t survive module reloads or redefinitions
- Can conflict if multiple notebooks share the same kernel
- Still requires manual state resets in tests
We should move the “only-once” guard into the browser DOM/JS layer so that
every call to format_html can blindly emit the header scripts/styles, but the
browser will insert them only once per page.
## Proposed Change:
1. Remove the _styles_loaded class variable and related Python guard logic.
2. Always call _build_html_header() and _get_javascript() on each
format_html.
3. Inside those methods, wrap the CSS/JS in small <script> blocks that:
- Check document.getElementById('df-styles') (or a global flag) before
appending a <style> tag
- Check a window.__df_formatter_js_loaded__ flag before defining the toggle
function
### example snippet:
```python
--- a/python/datafusion/dataframe_formatter.py
+++ b/python/datafusion/dataframe_formatter.py
@@ -XXX,XX +XXX,XX @@ class DataFrameHtmlFormatter:
- # Class var: _styles_loaded = False
def _build_html_header(self) -> list[str]:
- html = []
- # Only include styles and scripts if needed
- if include_styles:
- html.extend(self._build_css_and_script())
- if self.use_shared_styles:
- DataFrameHtmlFormatter._styles_loaded = True
- return html
+ return ["""
<script>
// Only inject CSS once per page
if (!document.getElementById('df-styles')) {
const style = document.createElement('style');
style.id = 'df-styles';
style.textContent = `
/* DataFrameHtmlFormatter CSS… */
`;
document.head.appendChild(style);
}
</script>
"""] + ([f"<style>{self.custom_css}</style>"] if self.custom_css else [])
def _get_javascript(self) -> str:
- return """
-<script> …existing JS… </script>
-"""
+ return """
<script>
// Only inject toggle logic once
if (!window.__df_formatter_js_loaded__) {
window.__df_formatter_js_loaded__ = true;
window.toggleDataFrameCellText = function(table_uuid, row, col) {
/* …existing toggle logic… */
};
}
</script>
"""
```
## Benefits:
- Guaranteed “inject once” directly in the browser, regardless of Python
reloads
- Simplifies Python state—no _styles_loaded flag to manage
- Safe in multi-notebook or testing scenarios
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