BagItUtils

This repository contains a python library along with a command line interface for creating, interacting with, and validating files in the BagIt-format (v1.0). It implements most but not all of the specification (see planned additions). The package consists of two major modules:

• bagit: basic support for the BagIt-spec including parsing (meta-)data and validating structure as well as checksums
• validator: an implementation of the BagIt Profiles-project's (1.4) specification for extended Bag validation; takes a modular approach for easy customization (see details)

Please refer to the examples-section for a brief overwiew of the features.

Key features of this repository are

• a modern, extendable, and easy to use API,
• a high test-coverage, and
• a command line interface.

Install

Install this package by entering

pip install bagit-utils

It is generally recommended to install in a virtual environment, create and activate said environment by entering for example

python3 -m venv venv
source venv/bin/activate

Basic usage examples

CLI

This package provides a command line interface (via the befehl-library) if installed with the extra-dependency "cli":

pip install bagit-utils[cli]

After installing, the CLI can be invoked with bagit. The CLI provides options for the creation, inspection, modification, and validation of Bags.

You can also activate autocomplete for (the current session of) bash-terminals with

eval "$(_BEFEHL_COMPLETION= bagit --generate-autocomplete)"

If you want to set up persistent autocomplete, instead generate the source file via

_BEFEHL_COMPLETION= bagit --generate-autocomplete

and place the contents of that script in your ~/.bash_autocomplete-file.

BagIt

Initialize an existing Bag with

from pathlib import Path
from bagit_utils import Bag

bag = Bag(Path("path/to/bag"))

Access bag-metadata via properties

print(bag.baginfo)
print(bag.manifests)
print(bag.tag_manifests)

Reload data after initialization

bag = Bag(Path("path/to/bag"))

# .. some operation that changes bag-info.txt

bag.load_baginfo()

Update manifests (on disk) after changes to the bag-payload/tag-files occurred

bag = Bag(Path("path/to/bag"))

# .. some operation that, e.g., adds/removes/changes files in data/ or meta/

bag.set_manifests()
bag.set_tag_manifests()

Update bag-info after initialization

bag = Bag(Path("path/to/bag"))

bag.set_baginfo(
    bag.baginfo | {"AdditionalField": ["value0", "value1"]}
)

Create bag from source

bag = Bag.build_from(
    Path("path/to/source"),  # should contain payload in data/-directory
    Path("path/to/bag"),  # should be empty
    baginfo={
        "Source-Organization": ["My Organization"].
        ...,
        "Payload-Oxum": [Bag.get_payload_oxum(Path("path/to/source"))],
        "Bagging-Date": [Bag.get_bagging_date()],
    },
    algorithms=["md5", "sha1"],
)

If a Bag is created with the load-flag or created via Bag.build_from with the validate-flag, the contents of the directory/created Bag are validated regarding the BagIt-specification (1.0) (Bag format or Bag format and file checksums, respectively). This validation can also be triggered manually by entering

report = bag.validate()

The report that is returned contains an overall flag for validity and a list of detected issues. For more advanced validation, see also the following section on Profile-Validation.

Customization

This section shows a simple example on how to extend the Bag class with custom loading- and validation-features.

Suppose Bags are expected to always contain a specific tag-file bag.json and the contents of this file should be available after instantiating a Bag.

To achieve this behavior, both the loading and validation can be hooked via the methods

• custom_load_hook,
• custom_validate_format_hook, and
• custom_validate_hook.

The updated loading for a corresponding CustomBag-class could then be defined as follows:

from json import loads
from bagit_utils import Bag

class CustomBag(Bag):
    def custom_load_hook(self):
        self.bag_json = loads((self.path / "bag.json").read_bytes())

Similarly, the required validation can be implemented as:

from bagit_utils.common import ValidationReport, Issue

class CustomBag(Bag):
    def custom_load_hook(self):
        ...

    def custom_validate_format_hook(self):
        report = ValidationReport(True, bag=self)

        if not (self.path / "bag.json").is_file():
            report.valid = False
            report.issues.append(
                Issue(
                    "error",
                    f"Missing file 'bag.json' in Bag at '{self.path}'.",
                    "bag.json",
                )
            )

        # additional validation steps
        # ...

        return report

BagIt-profile validation

The bagit_utils.validator-module consists of two classes that can be used for advanced Bag-validation and is based on the BagIt Profiles-project (1.4). Their implementation takes a modular approach to simplify customization.

BagItProfileValidator: A customizable validator for BagIt-profiles themselves

In order to load and validate a JSON-profile, run for example

from bagit_utils import BagItProfileValidator

profile = BagItProfileValidator.load_profile(profile_src="https://raw.githubusercontent.com/bagit-profiles/bagit-profiles/master/bagProfileFoo.json")

A ValueError will be raised if a problem is detected during validation of that profile.

BagValidator: A customizable validator for Bags based on BagIt-profiles

Using a BagIt-JSON-profile, the class BagValidator can be used to validate a Bag's contents (structure and metadata) in great detail. To run validation on a Bag-instance using the previously loaded profile, simply enter

from bagit_utils import BagValidator

report = BagValidator.validate_once(bag, profile=profile)

Just like the basic validation of the Bag, the response is a ValidationReport detailing validity and issues.

The validator can also be initialized only once and then be reused by instead writing

validator = BagValidator(profile=profile)
report1 = validator.validate(bag1)
report2 = validator.validate(bag2)
# ...

Validator customization

This section shows a simple example on how to extend the BagItProfileValidator and BagValidator classes.

Consider an extended BagIt-profile specification should be supported. For simplicity, the following will use the simple example of a boolean profile-tag My-Tag, which is required in the profile and, if set to true, requires the Bag to include a tag-file my-tag.txt.

The updated BagItProfileValidator could then be defined as follows:

class MyBagItProfileValidator(BagItProfileValidator):
    _ACCEPTED_PROPERTIES = BagItProfileValidator._ACCEPTED_PROPERTIES + ["My-Tag"]
    @classmethod
    def custom_validation_hook(cls, profile):
        if "My-Tag" not in profile:
            raise ValueError(cls._ERROR_PREFIX + "Missing required tag 'My-Tag'.")
        cls._handle_type_validation(bool, "My-Tag", profile["My-Tag"])

Similarly, the BagValidator also has a hook that can be used to implement the Bag-validation itself:

from bagit_utils.common import Issue, ValidationReport
class MyBagValidator(BagValidator):
    _PROFILE_VALIDATOR = MyBagItProfileValidator
    @classmethod
    def custom_validation_hook(cls, bag, profile):
        result = ValidationReport(True)
        if profile["My-Tag"] and not (bag.path / "my-tag.txt").is_file():
            result.valid = False
            result.issues.append(
                Issue("error", "Bag must contain tag-file 'my-tag.txt'.", "My-Tag")
            )
        return result

With these definitions, a validation using the changed specification can be run via

report = MyBagValidator.validate_once(bag, profile={"My-Tag": True})

The hooks available for these kinds of extensions are

• BagItProfileValidator._validate_baginfo_custom_item_hook
• BagItProfileValidator.custom_validation_hook
• BagValidator._validate_baginfo_custom_tags_hook
• BagValidator.custom_validation_hook Please refer to the source code for even more details on/documentation of arguments and expected behavior/return values.

Extensions of/Deviations from specification

In some minor aspects, these validators deviate from the BagIt-profiles specification:

• items in the "Bag-Info"-section of the profile support the additional field "regex" which enables optional regex-matching (using the fullmatch-strategy)
• the "BagIt-Profile-Info"-section is not validated
• the tag "BagIt-Profile-Identifier"-tag in bag-info.txt is not validated
• the "Accept-BagIt-Version"-section can be omitted which is then interpreted as it having the value ["1.0"]

Planned additions

• support for fetch.txt (currently validation only)
• support for Bag-serialization

Tests

The project has a high test-coverage. To run the tests locally, first install the dependencies

pip install .
pip install -r dev-requirements.txt

and afterwards run pytest with

pytest -v -s tests