daffy 0.2.0

Function decorators for Pandas Dataframe column name and data type validation

DAFFY DataFrame Column Validator

Description

In projects using Pandas, it's very common to have functions that take Pandas DataFrames as input or produce them as output. It's hard to figure out quickly what these DataFrames contain. This library offers simple decorators to annotate your functions so that they document themselves and that documentation is kept up-to-date by validating the input and output on runtime.

Table of Contents

• Installation
• Usage
• Contributing
• Tests
• License

Installation

Install with your favorite Python dependency manager like

pip install daffy

or

poetry add daffy

Usage

Start by importing the needed decorators:

from daffy import df_in, df_out

To check a DataFrame input to a function, annotate the function with @df_in. For example the following function expects to get a DataFrame with columns Brand and Price:

@df_in(columns=["Brand", "Price"])
def process_cars(car_df):
    # do stuff with cars

If your function takes multiple arguments, specify the field to be checked with it's name:

@df_in(name="car_df", columns=["Brand", "Price"])
def process_cars(year, style, car_df):
    # do stuff with cars

To check that a function returns a DataFrame with specific columns, use @df_out decorator:

@df_out(columns=["Brand", "Price"])
def get_all_cars():
    # get those cars
    return all_cars_df

To check both input and output, just use both annotations on the same function:

@df_in(columns=["Brand", "Price"])
@df_out(columns=["Brand", "Price"])
def filter_cars(car_df):
    # filter some cars
    return filtered_cars_df

If you want to also check the data types of each column, you can replace the column array:

columns=["Brand", "Price"]

with a dict:

columns={"Brand": "object", "Price": "int64"}

This will not only check that the specified columns are found from the DataFrame but also that their dtype is the expected.

Contributing

Contributions are accepted. Include tests in PR's.

Development

To run the tests, clone the repository, install dependencies with Poetry and run tests with PyTest:

poetry install
poetry shell
pytest

To enable linting on each commit, run pre-commit install. After that, your every commit will be checked with isort, black and flake8.

License

MIT