_images/pandera-logo.svg

Pandera

A flexible and expressive pandas validation library.

Why?

pandas data structures hide a lot of information, and explicitly validating them at runtime in production-critical or reproducible research settings is a good idea. pandera enables users to:

  1. Check the types and properties of columns in a pa.DataFrame or values in a pa.Series.
  2. Perform more complex statistical validation like hypothesis testing.
  3. Seamlessly integrate with existing data analysis/processing pipelines via function decorators.

pandera provides a flexible and expressive API for performing data validation on tidy (long-form) and wide data to make data processing pipelines more readable and robust.

Install

pip install pandera

Quick Start

import pandas as pd
import pandera as pa

from pandera import Column, DataFrameSchema, Check


# validate columns
schema = DataFrameSchema({
    # the check function expects a series argument and should output a boolean
    # or a boolean Series.
    "column1": Column(pa.Int, Check(lambda s: s <= 10)),
    "column2": Column(pa.Float, Check(lambda s: s < -1.2)),
    # you can provide a list of validators
    "column3": Column(pa.String, [
        Check(lambda s: s.str.startswith("value")),
        Check(lambda s: s.str.split("_", expand=True).shape[1] == 2)
    ]),
})

df = pd.DataFrame({
    "column1": [1, 4, 0, 10, 9],
    "column2": [-1.3, -1.4, -2.9, -10.1, -20.4],
    "column3": ["value_1", "value_2", "value_3", "value_2", "value_1"],
})

validated_df = schema.validate(df)
print(validated_df)
   column1  column2  column3
0        1     -1.3  value_1
1        4     -1.4  value_2
2        0     -2.9  value_3
3       10    -10.1  value_2
4        9    -20.4  value_1

Alternatively, you can pass strings representing the legal pandas datatypes:

schema = DataFrameSchema({
    "column1": Column("int64", Check(lambda s: s <= 10)),
    "column2": Column("float64", Check(lambda s: s < -1.2)),
    "column3": Column("object", [
        Check(lambda s: s.str.startswith("value")),
        Check(lambda s: s.str.split("_", expand=True).shape[1] == 2)
    ]),
})

Informative Errors

If the dataframe does not pass validation checks, pandera provides useful error messages. An error argument can also be supplied to Check for custom error messages.

In the case that a validation Check is violated:

import pandas as pd

from pandera import Column, DataFrameSchema, Int, Check

simple_schema = DataFrameSchema({
    "column1": Column(
        Int, Check(lambda x: 0 <= x <= 10, element_wise=True,
                   error="range checker [0, 10]"))
})

# validation rule violated
fail_check_df = pd.DataFrame({
    "column1": [-20, 5, 10, 30],
})

simple_schema.validate(fail_check_df)
Traceback (most recent call last):
...
pandera.SchemaError: <Schema Column: 'column1' type=int64> failed element-wise validator 0:
<lambda>: range checker [0, 10]
failure cases:
             index  count
failure_case
-20            [0]      1
 30            [3]      1

And in the case of a mis-specified column name:

# column name mis-specified
wrong_column_df = pd.DataFrame({
   "foo": ["bar"] * 10,
   "baz": [1] * 10
})

simple_schema.validate(wrong_column_df)
Traceback (most recent call last):
...
pandera.SchemaError: column 'column1' not in dataframe
   foo  baz
0  bar    1
1  bar    1
2  bar    1
3  bar    1
4  bar    1

Contributing

All contributions, bug reports, bug fixes, documentation improvements, enhancements and ideas are welcome.

A detailed overview on how to contribute can be found in the contributing guide on GitHub.

Indices and tables