py-tree-sitter

This module provides Python bindings to the tree-sitter parsing library.

Installation

This package currently only works with Python 3. There are no library dependencies, but you do need to have a C compiler installed.

pip3 install tree_sitter

Usage

Setup

First you'll need a Tree-sitter language implementation for each language that you want to parse. You can clone some of the existing language repos or create your own:

git clone https://github.com/tree-sitter/tree-sitter-go
git clone https://github.com/tree-sitter/tree-sitter-javascript
git clone https://github.com/tree-sitter/tree-sitter-python

Use the Language.build_library method to compile these into a library that's usable from Python. This function will return immediately if the library has already been compiled since the last time its source code was modified:

from tree_sitter import Language, Parser

Language.build_library(
  # Store the library in the `build` directory
  'build/my-languages.so',

  # Include one or more languages
  [
    'vendor/tree-sitter-go',
    'vendor/tree-sitter-javascript',
    'vendor/tree-sitter-python'
  ]
)

Load the languages into your app as Language objects:

GO_LANGUAGE = Language('build/my-languages.so', 'go')
JS_LANGUAGE = Language('build/my-languages.so', 'javascript')
PY_LANGUAGE = Language('build/my-languages.so', 'python')

Basic Parsing

Create a Parser and configure it to use one of the languages:

parser = Parser()
parser.set_language(PY_LANGUAGE)

Parse some source code:

tree = parser.parse(bytes("""
def foo():
    if bar:
        baz()
""", "utf8"))

If you have your source code in some data structure other than a bytes object, you can pass a "read" callable to the parse function.

The read callable can use either the byte offset or point tuple to read from buffer and return source code as bytes object. An empty bytes object or None terminates parsing for that line. The bytes must encode the source as UTF-8.

For example, to use the byte offset:

src = bytes("""
def foo():
    if bar:
        baz()
""", "utf8")

def read_callable(byte_offset, point):
    return src[byte_offset:byte_offset+1]

tree = parser.parse(read_callable)

And to use the point:

src_lines = ["def foo():\n", "    if bar:\n", "        baz()"]

def read_callable(byte_offset, point):
    row, column = point
    if row >= len(src_lines) or column >= len(src_lines[row]):
        return None
    return src_lines[row][column:].encode('utf8')

tree = parser.parse(read_callable)

Inspect the resulting Tree:

root_node = tree.root_node
assert root_node.type == 'module'
assert root_node.start_point == (1, 0)
assert root_node.end_point == (3, 13)

function_node = root_node.children[0]
assert function_node.type == 'function_definition'
assert function_node.child_by_field_name('name').type == 'identifier'

function_name_node = function_node.children[1]
assert function_name_node.type == 'identifier'
assert function_name_node.start_point == (1, 4)
assert function_name_node.end_point == (1, 7)

assert root_node.sexp() == "(module "
    "(function_definition "
        "name: (identifier) "
        "parameters: (parameters) "
        "body: (block "
            "(if_statement "
                "condition: (identifier) "
                "consequence: (block "
                    "(expression_statement (call "
                        "function: (identifier) "
                        "arguments: (argument_list))))))))"

Walking Syntax Trees

If you need to traverse a large number of nodes efficiently, you can use a TreeCursor:

cursor = tree.walk()

assert cursor.node.type == 'module'

assert cursor.goto_first_child()
assert cursor.node.type == 'function_definition'

assert cursor.goto_first_child()
assert cursor.node.type == 'def'

# Returns `False` because the `def` node has no children
assert not cursor.goto_first_child()

assert cursor.goto_next_sibling()
assert cursor.node.type == 'identifier'

assert cursor.goto_next_sibling()
assert cursor.node.type == 'parameters'

assert cursor.goto_parent()
assert cursor.node.type == 'function_definition'

Editing

When a source file is edited, you can edit the syntax tree to keep it in sync with the source:

tree.edit(
    start_byte=5,
    old_end_byte=5,
    new_end_byte=5 + 2,
    start_point=(0, 5),
    old_end_point=(0, 5),
    new_end_point=(0, 5 + 2),
)

Then, when you're ready to incorporate the changes into a new syntax tree, you can call Parser.parse again, but pass in the old tree:

new_tree = parser.parse(new_source, tree)

This will run much faster than if you were parsing from scratch.

The Tree.get_changed_ranges method can be called on the old tree to return the list of ranges whose syntactic structure has been changed:

for changed_range in tree.get_changed_ranges(new_tree):
    print('Changed range:')
    print(f'  Start point {changed_range.start_point}')
    print(f'  Start byte {changed_range.start_byte}')
    print(f'  End point {changed_range.end_point}')
    print(f'  End byte {changed_range.end_byte}')

Pattern-matching

You can search for patterns in a syntax tree using a tree query:

query = PY_LANGUAGE.query("""
(function_definition
  name: (identifier) @function.def)

(call
  function: (identifier) @function.call)
""")

captures = query.captures(tree.root_node)
assert len(captures) == 2
assert captures[0][0] == function_name_node
assert captures[0][1] == "function.def"

The Query.captures() method takes optional start_point, end_point, start_byte and end_byte keyword arguments which can be used to restrict the query's range. Only one of the ..._byte or ..._point pairs need to be given to restrict the range. If all are omitted, the entire range of the passed node is used.