DataExcept

DataExcept is a production-ready Python library that provides structured, hierarchical exception classes specifically designed for data science, machine learning, and data engineering workflows. Stop debugging generic ValueErrors and RuntimeErrors -- get meaningful, actionable error messages that help you understand exactly what went wrong in your data pipeline.

🚀 Why DataExcept?

❌ Without DataExcept	✅ With DataExcept
ValueError: Invalid value	DataValidationError: [DataValidationError:age] Invalid value for 'age': -1
RuntimeError: Training failed	ConvergenceError: [ConvergenceError] Model 'RandomForest' failed to converge after 100 iterations
Exception: Prediction error	ModelInferenceError: [ModelInferenceError:CNN] Inference failed for model 'CNN': CUDA out of memory
KeyError: column not found	MissingColumnError: [MissingColumnError] Missing required column 'customer_id' in DataFrame 'sales_data'

🎯 Key Features

• 🏗️ Hierarchical Structure: Catch one specific error, a whole domain, or every operational error via DataExceptError
• 📦 One Import: Every exception is available from dataexcept directly, or from its domain module — same objects either way
• 📊 Data Science Focused: 100 exception classes covering ML pipelines, feature engineering, model training
• 🔧 Production Ready: Logging helpers, error context, and exceptions that pickle — so they cross a process boundary with their message, attributes and cause intact
• 📚 Academic Quality: Proper documentation, type hints, and citation support
• 🐍 Python 3.10 – 3.14: Every supported version tested in CI, with full type safety
• 🧪 Well Tested: Full branch coverage of the package gated in CI, with contract tests over every exception class

📦 Quick Installation

pip install DataExcept

For development:

git clone https://github.com/DiogoRibeiro7/DataExcept.git
cd DataExcept
poetry install

🏃‍♂️ Quick Start

Basic Usage

from dataexcept import DataLoadingError, ModelTrainingError, ValidationError
import pandas as pd

# Data validation with context
def validate_dataframe(df: pd.DataFrame) -> None:
    if 'customer_id' not in df.columns:
        raise ValidationError(
            field='customer_id',
            value=list(df.columns),
            message="Customer ID column is required for processing"
        )

# Model training with specific error types
def train_model(model_type: str, epochs: int) -> None:
    try:
        # Your training code here
        if epochs > 1000:
            raise ModelTrainingError(
                model_type=model_type, 
                epoch=epochs,
                message=f"Training {model_type} exceeded reasonable epoch limit"
            )
    except Exception as e:
        # Wrap unknown errors with context
        raise ModelTrainingError(model_type, message=f"Unexpected error: {e}")

# File operations with detailed context
def load_dataset(file_path: str) -> pd.DataFrame:
    try:
        return pd.read_csv(file_path)
    except FileNotFoundError as e:
        raise DataLoadingError(source=file_path, original=e)

Exception Hierarchies

from dataexcept import ConvergenceError, DataExceptError, ModelTrainingError

try:
    # Your ML pipeline
    train_complex_model()
except ConvergenceError:
    # Handle specific convergence issues
    logger.warning("Model didn't converge, trying with different parameters")
    train_with_fallback_params()
except ModelTrainingError:
    # Handle any training-related error
    logger.error("Training failed, falling back to simpler model")
    train_simple_model()
except DataExceptError:
    # Handle anything else DataExcept raised
    logger.error("Job failed, notifying administrators")
    send_alert()

🏗️ Exception Categories

📊 Data Science & ML

from dataexcept.datascience_exceptions import *

# Data ingestion and validation
DataLoadingError("data.csv", FileNotFoundError())
DataValidationError("age", -5, "Age cannot be negative")
MissingDataError("income", "Required for credit scoring")

# Feature engineering and preprocessing
FeatureEngineeringError("log_transform", "Cannot take log of negative values")
DataNormalizationError("StandardScaler", "Division by zero in variance calculation")
DataImbalanceError(ratio=0.05, threshold=0.1)

# Model training and evaluation
ModelTrainingError("RandomForest", epoch=45)
ConvergenceError("GradientBoosting", iterations=1000)
OverfittingError(train_metric=0.98, val_metric=0.65)
BiasDetectionError("gender", bias_score=0.15, threshold=0.1)

# Model deployment and inference
ModelInferenceError("CNN", RuntimeError("CUDA out of memory"))
ModelCompatibilityError("2.1.0", "1.8.0")

🔧 Data Engineering & ETL

from dataexcept.dataengineering_exceptions import *

ETLJobError("daily_customer_pipeline")
SchemaEvolutionError("v2.1", reason="Incompatible column type change")
DataTransformationError("currency_conversion", "Invalid exchange rate")
BatchProcessingError("batch_2023_11_13", original=TimeoutError())

🐼 Pandas Operations

from dataexcept.pandas_exceptions import *

MissingColumnError("customer_id", dataframe="sales_df")
DtypeMismatchError("revenue", expected=["float64", "int64"], found="object")
MergeKeyError(["customer_id"], ["cust_id"])

🔗 Infrastructure & Networking

from dataexcept.network_exceptions import *
from dataexcept.database_exceptions import *

HostUnreachableError("api.example.com")
DatabaseConnectionError("postgresql://prod-db:5432/analytics")
QueryExecutionError("SELECT * FROM large_table", original=TimeoutError())

🔍 Advanced Features

Smart Logging Integration

from dataexcept.logging_helpers import log_and_raise, log_exception
import logging

logger = logging.getLogger(__name__)

# Context manager for automatic logging
with log_and_raise(logger=logger, context={"job_id": "ETL_001", "batch": "2023-11-13"}):
    process_daily_batch()

# Manual exception logging with context
try:
    risky_operation()
except Exception as exc:
    log_exception(
        exc, 
        logger=logger,
        context={"user_id": "12345", "operation": "feature_extraction"}
    )
    raise

Command Line Interface

# List every exception class the package exports (100 of them, alphabetically)
$ dataexcept list
ApiError
AuthenticationError
AuthorizationError
BatchProcessingError
BiasDetectionError
...

# Check the installed version
$ dataexcept --version
dataexcept <installed version>

🎯 Use Cases

🏭 Production ML Pipelines

• Model Training: Distinguish between convergence issues, data problems, and infrastructure failures
• Feature Engineering: Track which transformation steps fail and why
• Model Serving: Provide actionable error messages for inference failures
• Data Drift: Alert when model assumptions are violated

📈 Data Engineering

• ETL Pipelines: Clear error categorization for debugging complex data flows
• Data Quality: Structured validation errors with field-level context
• Schema Evolution: Track migration failures and compatibility issues
• Batch Processing: Identify whether failures are data-related or system-related

🔬 Research & Academia

• Reproducible Experiments: Consistent error handling across research codebases
• Citation Support: Proper academic attribution with CITATION.cff
• Documentation: Auto-generated API docs with comprehensive examples

📚 Real-World Example

"""
Complete ML pipeline with DataExcept error handling
"""
import numpy as np
import pandas as pd
from sklearn.ensemble import RandomForestClassifier
from dataexcept import ValidationError
from dataexcept.datascience_exceptions import *
from dataexcept.pandas_exceptions import *
from dataexcept.logging_helpers import log_and_raise
import logging

def ml_pipeline(data_path: str, target_col: str):
    logger = logging.getLogger(__name__)

    with log_and_raise(logger=logger, context={"pipeline": "customer_churn"}):
        # 1\. Data Loading
        try:
            df = pd.read_csv(data_path)
        except FileNotFoundError as e:
            raise DataLoadingError(source=data_path, original=e)

        # 2\. Data Validation
        if target_col not in df.columns:
            raise MissingColumnError(target_col, dataframe="training_data")

        if df[target_col].dtype not in ['int64', 'bool']:
            raise DtypeMismatchError(
                target_col, 
                expected=['int64', 'bool'], 
                found=str(df[target_col].dtype)
            )

        # 3\. Data Quality Checks
        missing_ratio = df.isnull().sum().sum() / (df.shape[0] * df.shape[1])
        if missing_ratio > 0.3:
            raise DataValidationError(
                field="missing_data_ratio",
                value=missing_ratio,
                message=f"Dataset has {missing_ratio:.1%} missing values, exceeds 30% threshold"
            )

        # 4\. Class Imbalance Check
        class_ratio = df[target_col].value_counts().min() / df[target_col].value_counts().max()
        if class_ratio < 0.1:
            raise DataImbalanceError(ratio=class_ratio, threshold=0.1)

        # 5\. Feature Engineering
        try:
            df['log_revenue'] = np.log(df['revenue'] + 1)
        except Exception as e:
            raise FeatureEngineeringError("log_transform", cause=str(e))

        # 6\. Model Training
        try:
            model = RandomForestClassifier(n_estimators=100)
            X = df.drop(columns=[target_col])
            y = df[target_col]
            model.fit(X, y)
        except Exception as e:
            raise ModelTrainingError("RandomForest", message=f"Training failed: {e}")

        # 7\. Model Validation
        train_score = model.score(X, y)
        if train_score < 0.6:
            raise UnderfittingError(train_metric=train_score, threshold=0.6)

        return model

# Usage
if __name__ == "__main__":
    try:
        model = ml_pipeline("customer_data.csv", "churned")
        print("✅ Pipeline completed successfully!")
    except DataLoadingError as e:
        print(f"❌ Data loading failed: {e}")
    except MissingColumnError as e:
        print(f"❌ Schema validation failed: {e}")
    except DataImbalanceError as e:
        print(f"⚠️  Data quality issue: {e}")
    except ModelTrainingError as e:
        print(f"❌ Model training failed: {e}")
    except Exception as e:
        print(f"💥 Unexpected error: {e}")

🤝 Contributing

We welcome contributions! See our Contributing Guide for details.

# Development setup
git clone https://github.com/DiogoRibeiro7/DataExcept.git
cd DataExcept
make install          # poetry install --with dev,docs
pre-commit install

make check            # lint, formatting, mypy and tests - everything CI runs
make help             # list all targets

Please also read the Code of Conduct. Security issues go through SECURITY.md, not the public issue tracker.

📖 Documentation

• Full Documentation: diogoribeiro7.github.io/DataExcept
• API Reference: API Docs
• API Stability: What is public and what may change
• Upgrading from 0.x: Migration guide
• Advanced Usage: Advanced Guide
• CLI Reference: CLI Guide
• Changelog: CHANGELOG.md

🎓 Citation

If you use DataExcept in your research, please cite the exact release you used. The canonical release metadata is maintained in CITATION.cff.

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🏆 About the Author

Diogo Ribeiro is a Lead Data Scientist at Mysense.ai and researcher/instructor at ESMAD (Instituto Politécnico do Porto). With expertise in machine learning, statistical analysis, and production ML systems, he created DataExcept to solve real-world error handling challenges in data science workflows.

• 🔗 ORCID: 0009-0001-2022-7072
• 🌐 Website: diogoribeiro7.github.io
• 🏢 Affiliation: ESMAD - Instituto Politécnico do Porto

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