abnf

library2.9.0pypypi✓ verified 23d ago

ABNF is a Python package designed to generate parsers from Augmented Backus-Naur Form (ABNF) grammars, as specified in RFC 5234 and RFC 7405. While its primary use is to parse data defined in RFCs, it is capable of handling any valid ABNF grammar. The library originated from parsing HTTP headers in a web framework and has since been utilized in production environments. The current version is 2.4.1.

serialization http-networking

pip install abnf

package ↗

INSTALL

IMPORT

SIG · ABNF

abnf

serializationpythonv2.9.0

Install

1.6s avg

Import

116ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v2.9.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.118s · 18.3MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.6s · import 0.114s · 19MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

Rule

✓ from abnf import Rule

rfc7232

✓ from abnf.grammars import rfc7232

Example of importing a pre-defined RFC grammar.

Demonstrates how to create a custom ABNF rule and parse a string using a pre-defined grammar from the `abnf.grammars` module, such as RFC 7232.

from abnf import Rule from abnf.grammars import rfc7232 # Example 1: Creating a custom rule and parsing (simplified) # This demonstrates the structure, actual parsing needs a Rule instance. custom_rule_grammar_str = 'double-quoted-string = DQUOTE *(%x20-21 / %x23-7E / %x22.22) DQUOTE' custom_rule_instance = Rule.create(custom_rule_grammar_str) print(f"Created custom rule: {custom_rule_instance.name}") # Example 2: Parsing with a pre-defined RFC grammar src = 'W/"moof"' # Instantiate the ETag rule from rfc7232 grammar etag_rule = rfc7232.Rule('ETag') # Parse the source string node, start = etag_rule.parse(src) print(f"\nParsed ETag: {src}") print(f"Resulting AST node: {node}") print(f"Parsing started at index: {start}")

abnf --version

Debug

Known issues

breakingVersion 2.0.0 introduced significant changes to backtracking implementation, which constituted a breaking change in behavior. Code relying on previous backtracking mechanisms may need adjustment.

fix

Review grammar definitions and parsing logic for compatibility with the new backtracking implementation. Test thoroughly.

affects: >=2.0.0

gotchaAs of version 2.0.0, `Repetition` objects utilize an LRU cache (`ParseCache`) to store parse results, but the initial implementation does not set maximum sizes for these caches. This can lead to unbounded memory growth and long-term performance issues in applications with extensive or long-running parsing tasks.

fix

Monitor memory usage and consider contributing feedback or implementing custom cache management if performance degradation is observed. Consult the library's GitHub for potential updates or configuration options related to cache sizing.

affects: >=2.0.0

gotchaWhen loading grammars from text files using `Rule.from_file`, ABNF strictly expects CRLF (Carriage Return Line Feed) as a delimiter for rules. Many text editors silently convert CRLF to LF (Line Feed only), which can cause parsing failures or unexpected behavior when the grammar file is read by the library.

fix

Ensure that grammar files provided to `Rule.from_file` explicitly use CRLF line endings. Verify line endings with a text editor that can display them (e.g., VS Code, Notepad++).

affects: All versions

gotchaThe library caches `Rule` objects (e.g., `Rule('rule-name')` will return the same object if the rule was previously created). While this behavior typically ensures consistency, the documentation advises against depending on it, suggesting that future versions or edge cases might alter this behavior.

fix

Avoid relying on `Rule('rule-name')` always returning the identical Python object. Treat rule instantiation as potentially returning a new, but functionally equivalent, object.

affects: All versions

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'abnf'

The 'abnf' package is not installed in the Python environment.

fix

Install the package using 'pip install abnf'.

NameError: name 'ABNF' is not defined

The 'ABNF' class or module is not imported or defined in the code.

fix

Ensure that 'ABNF' is correctly imported or defined before use.

ImportError: cannot import name 'Rule' from 'abnf'

The 'Rule' class is not available in the 'abnf' module, possibly due to version differences.

fix

Verify the installed version of 'abnf' and consult the documentation for the correct import statement.

from abnf import Rule

This is not an error string, but a common correct import. A common error associated would be `ImportError: cannot import name 'Rule' from 'abnf'` if the package is not found or installed incorrectly, or `NameError: name 'Rule' is not defined` if not imported.

fix

Ensure the 'abnf' package is installed and use `from abnf import Rule` to access the main Rule class.

ParseError: Parsing failed

The input string provided to the parser does not conform to the ABNF grammar defined, or the grammar itself contains errors.

fix

Review your ABNF grammar definition for correctness and ensure the input string strictly adheres to the specified grammar rules.

Upgrade

Version history

2.9.0latest on PyPI · released Aug 27, 2026

Audit

Dependencies

pythonrequiredRequired Python interpreter version.

Agent activity

57 hits · last 30 days

node

OpenAI (training)

Resources

packagehttps://pypi.org/project/abnf/ ↗