ast-pluckit 0.7.0

A fluent API for querying, viewing, and mutating source code — CSS selectors over ASTs, backed by DuckDB.

pluckit

A fluent API for querying, viewing, and mutating source code. CSS selectors over ASTs, backed by DuckDB.

pluckit lets you select code with CSS-like selectors, render it as formatted source regions, and apply structural mutations — all from a single fluent API or a compact CLI. Under the hood it's a thin Python layer over DuckDB with the sitting_duck AST extension, so queries compile to SQL and run against tree-sitter ASTs for 27 languages.

• Documentation: pluckit.readthedocs.io
• PyPI: ast-pluckit
• Changelog: CHANGELOG.md

Status: v0.1-alpha. Query, view, and mutate work end-to-end. Call graph, history, and scope plugins are v0.2.

Install

pip install ast-pluckit

The distribution name is ast-pluckit (the bare pluckit name was taken on PyPI by an abandoned 2019 project). The import name and CLI are still pluckit:

pluckit view ".fn#main" src/**/*.py

from pluckit import Plucker

For local development:

pip install -e .

pluckit needs DuckDB with the sitting_duck community extension. It will auto-install on first use, but you can also run:

pluckit init

to install and verify the extensions eagerly and get clearer diagnostics if anything fails.

The CLI

Full reference lives in the CLI docs. The short version:

View — render matched code regions as markdown

# Show the full body of a function
pluckit view ".fn#parse_chain" training/chain_parser.py

# Just the signature
pluckit view ".fn#parse_chain { show: signature; }" training/chain_parser.py

# First 10 lines
pluckit view ".fn#parse_chain { show: 10; }" training/chain_parser.py

# Class outline — header + method signatures
pluckit view ".cls#ChainSampler" training/chain_sampler.py

# Multi-rule query (CSS-stylesheet style)
pluckit view ".fn { show: signature; } #main { show: body; }" training/generate.py

# Read the query from stdin
echo ".fn[name^=test_] { show: signature; }" | pluckit view - tests/*.py

# Or from a file
pluckit view --query-file audit.q src/**/*.py

# Multiple paths and glob patterns
pluckit view ".fn#parse" src/*.py lib/*.py

When a signature-mode query matches more than one function, the output collapses into a markdown table — dramatically smaller than a code fence per match:

| File               | Lines   | Signature                                  |
|---|---|---|
| src/validate.py    | 35-54   | `def _is_garbled(intent: str) -> bool:`    |
| src/validate.py    | 73-88   | `def _flatten_ops(comp: Any) -> list[str]:`|
| src/validate.py    | 102-196 | `def validate_chain(chain: str) -> Result:`|

Find — list matches for scripting

find is the terse companion to view. It emits one line per match in formats designed for shell pipelines and agent tool-use:

# Default: file:line:name, one per line — feed directly into $(...)
pluckit find ".fn:exported" src/**/*.py

# Just the names — good for set operations
pluckit find ".fn[name^=test_]" --format names tests/*.py | sort -u

# Signature table — a lightweight audit view
pluckit find ".fn:exported" --format signature src/**/*.py

# Machine-readable JSON — one object per match
pluckit find ".cls" --format json src/**/*.py

# Just the total count
pluckit find ".fn" --count src/**/*.py

Edit — apply structural changes to matched nodes

All edits are transactional: if any affected file fails syntax re-validation after splicing, every file is rolled back to its pre-edit state. Use --dry-run to see how many matches each path would affect before writing.

# Replace a function's body entirely
pluckit edit ".fn#foo" --replace-with "def foo():\n    return 1" src/*.py

# Scoped find-and-replace within matched nodes (2-arg replace)
pluckit edit ".fn#validate" --replace "return None" "raise ValueError()" src/*.py

# Add a parameter to every matched function
pluckit edit ".fn:exported" --add-param "timeout: int = 30" src/**/*.py

# Remove a parameter by name
pluckit edit ".fn#fetch_user" --remove-param "cache" src/*.py

# Add a keyword argument at every call site (paired with --add-param above)
pluckit edit ".call#fetch_user" --add-arg "timeout=timeout" src/**/*.py

# Remove a keyword argument from every call site
pluckit edit ".call#fetch_user" --remove-arg "cache" src/**/*.py

# Remove matched nodes entirely
pluckit edit ".fn#deprecated_helper" --remove src/*.py

# Clear a function/class body to `pass` (Python) or `{}` (C-family)
pluckit edit ".fn#todo_later" --clear-body src/*.py

# Rename a definition (first name occurrence)
pluckit edit ".fn#old_name" --rename "new_name" src/*.py

# Insert lines at the top/bottom of matched function bodies
pluckit edit ".fn:exported" --prepend-lines "logger.debug('entered')" src/*.py
pluckit edit ".fn:exported" --append-lines  "logger.debug('exited')"  src/*.py

# Insert at a specific sibling position — anchor is a CSS selector
# resolved against each matched node's subtree (exact, not heuristic)
pluckit edit ".cls#Foo" --insert-lines before ".fn#bar" "def pre_bar(self): pass" src/*.py
pluckit edit ".cls#Foo" --insert-lines after  ".fn#bar" "def post_bar(self): pass" src/*.py
pluckit edit ".fn#main" --insert-lines before ".ret" "cleanup()" src/*.py

# Wrap matched nodes
pluckit edit ".call#query" --wrap "try:" "except DatabaseError:\n    raise" src/*.py

# See what would change without writing — prints a real unified diff
pluckit edit ".fn#foo" --remove --dry-run src/*.py

Chaining edits. Multiple operations can share a single group, and multiple (selector, operations) groups can run in one invocation, separated by --. This is how you keep an API and its call sites in sync atomically:

pluckit edit \
    ".cls#Foo .fn#__init__" --add-param "foo: int = 30" \
                            --append-lines "self.foo = foo" \
    -- \
    ".call#Foo"             --add-arg "foo=10" \
    src/**/*.py

The whole command is one transaction: if any group produces invalid syntax in any file, every affected file rolls back to its pre-edit state.

Line-level vs character-level edits. --prepend-lines, --append-lines, and --insert-lines all insert whole new lines at indentation-matched positions. The 2-arg --replace OLD NEW is the character-level equivalent — it does a string-level replace within the matched node's text, preserving the rest of each line verbatim. --replace-with replaces the entire node. Character-level --insert-chars for inline positional insertions is reserved for v0.2.

The Python API

from pluckit import Plucker, AstViewer

pluck = Plucker(code="src/**/*.py", plugins=[AstViewer])

# Query
fns = pluck.find(".fn:exported")
print(fns.count())                  # 47
print(fns.names()[:5])              # ['authenticate', 'decode_jwt', ...]

# View
print(pluck.view(".fn#validate_token { show: signature; }"))

# Mutate (v0.1)
pluck.find(".fn#validate_token").replaceWith(
    "return None",
    "raise ValueError('token required')",
)
pluck.find(".fn:exported").addParam("timeout: int = 30")

Module-level shortcuts

from pluckit import view

# One-shot viewer query — creates an ephemeral Plucker
print(view(".fn#main { show: outline; }", code="src/**/*.py"))

Selector syntax

Selectors mirror CSS but address AST nodes:

Syntax	Meaning
.fn	All function definitions (cross-language alias)
.cls, .class	All class definitions
.call	All call expressions
.fn#name	Function named name
.fn:exported	Public (non-underscore) functions
.fn[name^=test_]	Functions whose name starts with test_
.fn[name*=auth]	Functions whose name contains auth
.cls#Foo .fn	Functions inside class Foo
.fn:has(.call#execute)	Functions that call execute()
.fn:not(:has(.try))	Functions with no try block

sitting_duck's full selector language is richer than what pluckit currently compiles — see its docs for :calls(), :matches(), :scope(), and the call graph pseudo-elements. These work when you call ast_select directly against the underlying DuckDB connection; pluckit's fluent layer supports a growing subset.

Viewer show modes

The viewer supports a small declaration language — CSS declaration blocks attached to selectors:

Show value	Behavior
body	Full matched node text (default for functions, calls, statements)
signature	Declaration line only (synthesized from native AST metadata)
outline	Class header + method signatures + dataclass fields (default for classes)
enclosing	Walk up to the nearest scope and render that as body
N (number)	First N lines of the body with ... truncation marker

Rules compose like a stylesheet:

.fn { show: signature; }            /* default most functions to signature */
.fn#main { show: body; }            /* except main — show its full body    */
.cls#Config { show: outline; }      /* Config class with methods listed   */

Plugins

pluckit is composable. Core capabilities stay in Selection; anything that depends on extra data or infrastructure moves to a plugin:

from pluckit import Plucker, AstViewer

pluck = Plucker(
    code="src/**/*.py",
    plugins=[AstViewer],     # viewer with `show:` declarations
    # plugins=[Calls],       # call graph (v0.2)
    # plugins=[History],     # git history (v0.2)
    # plugins=[Scope],       # scope analysis (v0.2)
)

Plugins register new methods on Selection, new pseudo-classes for the selector compiler, and optional upgrades for existing methods (e.g., fledgling-python can upgrade callers() with import-resolved results).

Training data

The training/ directory contains a synthetic training data generator that produces (intent, chain) pairs for fine-tuning a small code model. It works entirely from the API spec in reference/api.yaml — no pluckit runtime needed. A ~40k-pair corpus (19% error-driven, 19% context-bearing) is committed via git LFS under training/.

See training/README.md for generation and formatting.

Architecture

   pluckit.Plucker              entry point, plugin registry, DuckDB context
        │
   pluckit.Selection            lazy DuckDB relation chain
        │                       query, filter, navigate, read, mutate
        ├── pluckit._sql        selector → SQL WHERE fragments
        │
   pluckit.plugins              optional capabilities
        ├── AstViewer           CSS-style viewer with `show:` declarations
        ├── Calls (v0.2)        call graph via name-join + plugin upgrades
        ├── History (v0.2)      git history via duck_tails
        └── Scope (v0.2)        read/write interface via flags byte
        │
   pluckit.mutation             byte-splice engine with transaction rollback
        └── pluckit.mutations   ReplaceWith, AddParam, Wrap, Rename, ...

All queries ultimately compile to SQL over sitting_duck's read_ast() table. Mutations read files, apply string-level splices at line granularity, re-parse to validate, and roll back on any syntax error.

Contributing

Run tests:

pip install -e ".[dev]"
pytest

189 tests covering selectors, the Selection API, the plugin system, the viewer, the CLI, and the mutation engine.