feature #49580: support new-style float_format string in to_csv #61650
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pedromfdiogo
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feat(to_csv): support new-style float_format strings using str.format
Detect and process new-style format strings (e.g., "{:,.2f}") in the
float_format parameter of to_csv.
- Check if float_format is a string and matches new-style pattern
- Convert it to a callable (e.g., lambda x: float_format.format(x))
- Ensure compatibility with NaN values and mixed data types
- Improves formatting output for floats when exporting to CSV
Example:
df = pd.DataFrame([1234.56789, 9876.54321])
df.to_csv(float_format="{:,.2f}") # now outputs formatted values like
1,234.57
Co-authored-by: Pedro Santos <pedro.filipe.santos@tecnico.ulisboa.pt>
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@simonjayhawkins Hi! Just wanted to check if this PR needs anything else from my side. Thanks in advance for reviewing |
mroeschke
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Jun 30, 2025
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| if fmt is None: | ||
| return None | ||
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| if callable(fmt): | ||
| return fmt |
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Suggested change
| if fmt is None: | |
| return None | |
| if callable(fmt): | |
| return fmt | |
| if fmt is None or callable(fmt): | |
| return fmt |
mroeschke
reviewed
Jun 30, 2025
| except (ValueError, KeyError, IndexError) as e: | ||
| raise ValueError(f"Invalid new-style format string {fmt!r}") from e | ||
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| # If fmt is neither None, nor callable, nor a successfully processed string, |
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| # If fmt is neither None, nor callable, nor a successfully processed string, |
mroeschke
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Jun 30, 2025
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| with warnings.catch_warnings(record=True): | ||
| warnings.simplefilter("always") |
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Please use tm.assert_produces_warning
mroeschke
reviewed
Jun 30, 2025
| else: | ||
| try: | ||
| _ = fmt.format(1.0) # Test with an arbitrary float | ||
| return lambda x: fmt.format(x) |
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| return lambda x: fmt.format(x) | |
| return fmt.format |
|
Could you add a whatsnew entry in |
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feat(to_csv): support new-style float_format strings using str.format
Detect and process new-style format strings (e.g., "{:,.2f}") in the float_format parameter of to_csv.
Example:
df = pd.DataFrame([1234.56789, 9876.54321])
df.to_csv(float_format="{:,.2f}") # now outputs formatted values like 1,234.57 and support new-style without .format
doc/source/whatsnew/v3.0.0.rstfile if fixing a bug or adding a new feature.