arnio 0.1.2

Fast CSV processing and data cleaning companion for pandas

arnio

Fast CSV loading and cleaning for Python, powered by C++.

arnio handles the slowest, most repetitive part of working with tabular data: reading a raw CSV file, cleaning it up, and getting it into a DataFrame. The parsing and cleaning run in C++ through pybind11. The output is a standard pandas DataFrame.

pip install arnio

import arnio as ar

# Load and clean in three lines
frame = ar.read_csv("customers.csv")

clean = ar.pipeline(frame, [
    ("strip_whitespace",),
    ("drop_nulls",),
    ("drop_duplicates",),
])

df = ar.to_pandas(clean)

Requires Python 3.9+. Wheels available for Linux, macOS, and Windows. Source builds require a C++17 compiler.

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How arnio is different

• CSV parsing runs in C++, not Python. On large files, ar.read_csv() uses measurably less time and memory than pd.read_csv.

• Cleaning is built in, not bolted on. ar.pipeline() takes a list of named steps and runs them in sequence. No scattered method chains, no copy-paste between notebooks.

• Preview before you load. ar.scan_csv("file.csv") returns column names and inferred types by sampling the file -- no full load required.

• Exact memory tracking. frame.memory_usage() returns real byte counts from C++. No estimation, no deep=True.

• Pandas is the output, not the engine. arnio reads and cleans your data natively, then hands you a DataFrame when you're ready.

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Performance

Benchmark: 1M-row CSV, 12 columns, mixed types.

Tool	Load time	Peak memory
pandas	~4.2s	~620 MB
arnio	~2.1s	~380 MB

Approximately 2x faster CSV ingestion and 40% lower peak memory on large files.

Measured on an M2 MacBook Pro, Python 3.11. Your results will vary. Benchmark with your own data.

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pandas vs arnio

pandas

import pandas as pd

df = pd.read_csv("sales.csv")

str_cols = df.select_dtypes(include="object").columns
df[str_cols] = df[str_cols].apply(lambda c: c.str.strip())

df = df.dropna()
df = df.drop_duplicates()

arnio

import arnio as ar

frame = ar.read_csv("sales.csv")

clean = ar.pipeline(frame, [
    ("strip_whitespace",),
    ("drop_nulls",),
    ("drop_duplicates",),
])

df = ar.to_pandas(clean)

Same result. Less code. Each step is explicit. The pipeline runs in C++.

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When to use arnio

Use arnio when your bottleneck is loading and cleaning CSVs -- large files, messy columns, repeated preprocessing across projects.

Use pandas when you need analysis -- groupby, merge, pivot, time-series, plotting. arnio produces DataFrames; everything downstream stays the same.

arnio replaces the first steps of your notebook. It does that part faster and with less code. Everything after that is still pandas.

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Roadmap

arnio is actively in development. The core CSV reader and basic cleaning primitives are the current focus. Planned work includes:

• C++ CSV parser core
• Basic cleaning API (drop_nulls, strip_whitespace, normalize_columns)
• pandas DataFrame output
• Streaming / chunked reads for very large files
• Type inference and automatic dtype casting
• Encoding detection and normalization
• Schema validation and column contracts
• Parallel parsing across CPU cores
• CLI tool (arnio clean data.csv --output clean.csv)
• Async-friendly API for use in async pipelines

Feedback on priorities is welcome — open a GitHub Discussion to share what matters most to you.

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Contributing

Contributions are welcome and genuinely appreciated. arnio is early-stage, which means there's real space to shape how it grows.

To get started:

git clone https://github.com/yourusername/arnio.git
cd arnio
pip install -e ".[dev]"

Before submitting a pull request:

• Run the test suite: pytest tests/
• Follow the existing code style (enforced via ruff)
• Keep PRs focused — one concern per pull request
• Open an issue first for significant changes so the direction can be discussed

There's a CONTRIBUTING.md with more detail on the development setup, C++ build process, and testing approach.

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License

arnio is released under the MIT License.

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Built to make Python data work feel faster and cleaner — one CSV at a time.