gast

library0.7.0pypypi✓ verified 52d ago

gast provides a compatibility layer between the Abstract Syntax Trees (AST) of various Python versions (including Python 2 and Python 3), offering a homogeneous API compatible with the standard library `ast` module. It abstracts away version-specific differences in the AST structure, making it easier to write tools that work across multiple Python versions. The library is currently at version 0.7.0 and remains actively maintained.

serialization devops

pip install gast

github ↗package ↗

Install & Compatibility

Where this runs

tested against v0.7.0 · 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 3.10–3.925 runs

installs and imports cleanly · install 0.0s · import 0.017s · 18MB

glibc

py 3.10–3.925 runs

installs and imports cleanly · install 1.5s · import 0.016s · 18MB

16MB installed

● package 16MB

Code

Verified usage

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

gast

✓ import gast

Node

✓ from gast import Name, Constant

gast provides all standard `ast` nodes, but some might be harmonized across versions (e.g., `gast.Constant`).

parse

✓ gast.parse(code)

✗ ast.parse(code) if expecting a GAST node

gast.parse directly produces a GAST node, unlike ast.parse which produces a standard AST node.

This quickstart demonstrates how to parse Python code into a `gast` AST, convert a `gast` AST to a standard `ast` module AST, and convert a standard `ast` to a `gast` AST. The `gast.dump` function is used for easy inspection of the GAST structure.

import gast import ast code = """def foo(x): return x + 1""" # Parse code into a GAST (Generic AST) node gast_tree = gast.parse(code) print("GAST Tree (using gast.dump):\n" + gast.dump(gast_tree)) # Convert the GAST tree to a standard AST tree for the current Python version std_ast_tree = gast.gast_to_ast(gast_tree) print("\nStandard AST Tree (from GAST, using ast.dump):\n" + ast.dump(std_ast_tree)) # Example of converting a standard AST to a GAST tree std_ast_input = ast.parse("a = 'hello'") gast_from_std = gast.ast_to_gast(std_ast_input) print("\nGAST Tree (from standard AST input, using gast.dump):\n" + gast.dump(gast_from_std))

Debug

Known issues

breakingFor Python 3.8 and later, several `ast` node types like `ast.Num`, `ast.Str`, `ast.Bytes`, `ast.Ellipsis`, and `ast.NamedConstant` are replaced by `gast.Constant` in `gast` ASTs (since `gast >= 0.3.0`). Code that directly inspects or creates these specific node types must be updated to use `gast.Constant` for cross-version compatibility.

fix

Replace usages of `gast.Num`, `gast.Str`, etc., with `gast.Constant(value=..., kind=None)` when working with GAST trees, especially when targeting Python 3.8+.

affects: gast >= 0.3.0, Python >= 3.8

gotchaThe representation of certain AST nodes changes in Python 3.9+. For instance, `ast.arg` nodes are represented as `ast.Name` with an `ast.Param` context, and `ExceptHandler.name` is an `ast.Name` with an `ast.Store` context instead of a simple string.

fix

When traversing or manipulating GASTs, be aware of these structural changes and use appropriate attribute access or type checks, or rely on `gast`'s conversion functions (`gast.gast_to_ast`, `gast.ast_to_gast`) to handle discrepancies.

affects: gast, Python >= 3.9

gotchaThe interpretation of literals like `None`, `True`, and `False` differs between Python 2 and Python 3. In Python 3, they are parsed as `gast.Constant`, while in Python 2, they are parsed as `gast.Name`.

fix

When writing tools that target both Python 2 and Python 3 via `gast`, ensure your code can handle these literals potentially being either `gast.Constant` or `gast.Name`.

affects: gast, Python 2 vs Python 3

gotchaWhile `gast` provides an API compatible with `ast`, directly importing or using classes from the standard `ast` module when you intend to work with `gast`'s cross-version AST can lead to unexpected behavior or `AttributeError` if the underlying `ast` module's structure for that node differs from `gast`'s harmonized representation.

fix

Always import and use node types directly from `gast` (e.g., `gast.Name`, `gast.Constant`) when building or manipulating GAST trees to ensure full compatibility and abstraction across Python versions.

affects: All versions

gotchaThe `_field_types` attribute, which exists for each AST class in standard `ast` modules, is always empty in `gast` for Python versions before 3.10. Relying on this field for introspection might yield incomplete information on older Python versions.

fix

Avoid relying on `_field_types` for critical logic if your tool needs to function correctly across a wide range of Python versions. Consider alternative introspection methods or conditional logic based on Python version.

affects: gast, Python < 3.10

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'gast'

The 'gast' library is not installed in the current Python environment or the Python interpreter cannot locate it in its search path.

fix

Install the 'gast' library using pip: `pip install gast` or ensure your environment variables (like PYTHONPATH) are correctly set if it's installed in a non-standard location.

AttributeError: module 'gast' has no attribute 'Num'

This error typically occurs when a dependent library (like an older version of TensorFlow) expects specific AST nodes (like `Num`, `Str`, `Bytes`) that have been deprecated and replaced by `gast.Constant` in newer `gast` versions (e.g., gast >= 0.3.0 or >= 0.4.0).

fix

Downgrade 'gast' to an older version compatible with the dependent library (e.g., `pip install gast==0.2.2` or `pip install gast==0.3.3`), or upgrade the dependent library to one that supports newer `gast` versions.

AttributeError: module 'gast' has no attribute 'Index'

Similar to the `Num` error, this indicates a breaking API change in 'gast' where the `Index` AST node (or its equivalent) was removed or modified in a newer version, while an older dependent package still tries to access it.

fix

Downgrade 'gast' to a version compatible with the problematic dependent library (e.g., `pip install gast==0.3.3`) or update the dependent library to one that supports the current 'gast' version.

python-gast03 and python-gast are in conflict

This is a package management conflict, often encountered with system package managers (like `pacman` on Arch Linux), where different installed packages require mutually exclusive versions of 'gast' (e.g., one requires `python-gast` and another `python-gast03`).

fix

Identify which packages require conflicting 'gast' versions. You may need to remove one of the conflicting packages, or use a virtual environment to isolate the dependencies, or check for updated packages that resolve the conflict (e.g., `sudo pacman -R python-gast` and then `sudo pacman -Syu` to allow the update to install `python-gast03`).

Upgrade

Version history

0.7.0latest on PyPI

Audit

Dependencies

PythonrequiredCore dependency for execution.

Agent activity

10 hits · last 30 days

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Resources

githubhttps://github.com/serge-sans-paille/gast ↗

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