Matchify

Matchify automatically converts eligible if/elif/else chains into Python 3.10+ match statements while preserving runtime behavior and source formatting.

Note

Matchify was built with assistance from AI tools. Its implementation and generated transformations may contain mistakes, so review changes and run your project's tests before relying on them. Feedback and bug reports are very welcome.

Examples

Simple equality chain:

# Before
if x == 1:
    print("one")
elif x == 2:
    print("two")
else:
    print("other")

# After
match x:
    case 1:
        print("one")
    case 2:
        print("two")
    case _:
        print("other")

isinstance with attributes:

# Before
if isinstance(node, Point) and node.x == 5:
    print("x is 5")
elif isinstance(node, Point):
    print("other point")

# After
match node:
    case Point(x=5):
        print("x is 5")
    case Point():
        print("other point")

Sequence patterns:

# Before
if len(point) == 2 and point[0] == 0 and point[1] == 1:
    print("origin offset")
elif len(point) == 2 and point[0] == 1:
    print("other pair")

# After
match point:
    case 0, 1:
        print("origin offset")
    case 1, _:
        print("other pair")

Nested patterns (isinstance inside sequences):

# Before
if len(x) == 2 and isinstance(x[0], Point) and x[1] == 2:
    print("point and 2")
elif len(x) == 2 and x[0] == 1 and x[1] == 1:
    print("ones")

# After
match x:
    case Point(), 2:
        print("point and 2")
    case 1, 1:
        print("ones")

Nested sequences:

# Before
if (
    len(data) == 2
    and len(data[0]) == 2
    and data[0][0] == 1
    and data[0][1] == 2
    and data[1] == 3
):
    print("nested list")
elif (
    len(data) == 2
    and isinstance(data[0], Point)
    and len(data[1]) == 2
    and data[1][0] == 0
    and data[1][1] == 0
):
    print("point with coordinates")

# After
match data:
    case [1, 2], 3:
        print("nested list")
    case Point(), [0, 0]:
        print("point with coordinates")

Class patterns with sequence attributes:

# Before
class Data:
    def __init__(self, value):
        self.value = value


obj = Data([1, 2, 3])
if (
    isinstance(obj, Data)
    and len(obj.value) == 3
    and obj.value[0] == 1
    and obj.value[1] == 2
    and obj.value[2] == 3
):
    print("data with list")
elif isinstance(obj, Data):
    print("other data")


# After
class Data:
    def __init__(self, value):
        self.value = value


obj = Data([1, 2, 3])
match obj:
    case Data(value=[1, 2, 3]):
        print("data with list")
    case Data():
        print("other data")

Installation

Install "matchify" as a command-line tool with uv:

uv tool install matchify

Or run it without installing:

uvx matchify path/to/project/

Key Features

• Automatic conversion of if/elif/else chains to Python 3.10+ match statements
• Preserves formatting and code structure using LibCST
• Supports multiple pattern types:
  • Literal comparisons (x == 1, x == "value")
  • Identity checks (x is None, x is True)
  • isinstance checks (isinstance(x, MyClass))
  • Class patterns with attributes (isinstance(p, Point) and p.x == 5)
  • Sequence patterns (len(x) == 2 and x[0] == 0 and x[1] == 1)
  • Nested sequences ([[1, 2], 3])
  • Sequence attributes in class patterns (Data(value=[1, 2, 3]))
  • Or patterns for isinstance tuples (isinstance(x, (int, float)))
• Parallel processing for fast conversion of large codebases
• Safe transformations - only converts when semantics are preserved

Usage

# Convert a single file
matchify path/to/file.py

# Convert all Python files in a directory
matchify path/to/project/

# Convert with verbose output
matchify path/to/project/ -v

# Check whether files would be converted without writing changes
matchify path/to/project/ --check

# Use parallel processing (default: number of CPUs)
matchify path/to/project/ -j 8

# Enable one risky assumption explicitly
matchify path/to/project/ --assume pure-subjects

# Disable all risky assumptions
matchify path/to/project/ --safe

# Enable all risky assumptions
matchify path/to/project/ --risky

pre-commit

Matchify provides two pre-commit hooks.

Use matchify to automatically rewrite files, similar to the default Black hook:

repos:
- repo: https://github.com/15r10nk/matchify
  rev: v0.1.0
  hooks:
  - id: matchify

Use matchify-check to only report files that would be converted without modifying them:

repos:
- repo: https://github.com/15r10nk/matchify
  rev: v0.1.0
  hooks:
  - id: matchify-check

Risky assumptions

By default, Matchify enables no risky assumptions. --safe makes that explicit. --risky enables all available risky assumptions. --safe is conservative, but it is not a formal guarantee that every rewrite preserves behavior. Python features such as custom equality, descriptors, and dynamic class behavior can still expose transformer bugs or semantic edge cases, so review the generated changes and run your project's tests. When a skipped if/elif chain would require a risky assumption, the CLI prints the file location and the required --assume value instead of converting that chain.

--assume=pure-subjects

Permits transformations such as a.x == 1 and b.y == 2 into a match on (a.x, b.y). This evaluates every subject eagerly, so enable it only when those name, attribute, and subscript reads cannot raise exceptions or produce observable side effects. Without the option, later and operands remain guards and preserve short-circuiting.

# Before
if a.x == 1 and b.y == 2:
    handle_first()
elif a.x == 3 and b.y == 4:
    handle_second()

# After
match (a.x, b.y):
    case 1, 2:
        handle_first()
    case 3, 4:
        handle_second()

--assume=use-object

Permits generic attribute patterns such as object(x=1) when different branches inspect attributes of a common object without an explicit isinstance check. This performs pattern-time attribute lookups, so enable it only when those lookups cannot raise exceptions or produce observable side effects.

# Before
if value.x == 1:
    handle_x()
elif value.y == 2:
    handle_y()

# After
match value:
    case object(x=1):
        handle_x()
    case object(y=2):
        handle_y()

--assume=identity-equality

Permits conversions from qualified identity comparisons such as op is Op.ADD to value patterns such as case Op.ADD. Match value patterns compare with equality, not identity, so enable it only when identity and equality are equivalent for those values.

# Before
if op is Op.ADD:
    add()
elif op is Op.SUB:
    subtract()

# After
match op:
    case Op.ADD:
        add()
    case Op.SUB:
        subtract()

--assume=hashable-subjects

Permits membership tests against literal sets to become OR patterns. Set membership hashes the subject and can raise TypeError for an unhashable value, while a pattern only performs equality comparisons. Enable it only when match subjects are hashable. Custom __hash__ and __eq__ implementations may still make lookup behavior or side effects differ from pattern matching.

# Before
if value in {1, 2}:
    handle_small()
elif value == 3:
    handle_three()

# After
match value:
    case 1 | 2:
        handle_small()
    case 3:
        handle_three()

--assume=list-sequence-pattern

Permits a sequence pattern to imply an explicit isinstance(value, list) check. Python sequence patterns can also match other sequence types, so enable it only when that broader match is acceptable.

# Before
if isinstance(value, list) and len(value) == 1 and value[0] == 1:
    handle_one()
elif value is None:
    handle_none()

# After
match value:
    case 1,:
        handle_one()
    case None:
        handle_none()

--assume=tuple-sequence-pattern

Permits a sequence pattern to imply an explicit isinstance(value, tuple) check. Python sequence patterns can also match other sequence types, so enable it only when that broader match is acceptable. Checks against (list, tuple) require both sequence assumptions.

# Before
if isinstance(value, tuple) and len(value) == 1 and value[0] == 1:
    handle_one()
elif value is None:
    handle_none()

# After
match value:
    case 1,:
        handle_one()
    case None:
        handle_none()

--assume=lookup-equality

Permits dictionary lookup tables embedded in statements to become match statements. Dictionary lookup uses hashing while patterns use equality, and dictionary values are evaluated only in the selected case instead of eagerly when constructing the dictionary. Enable it only when those equality and evaluation-order differences are acceptable. Tuple keys, including nested tuples, become sequence patterns and can therefore also match equivalent non-tuple sequences.

# Before
result = {"create": "POST", "read": "GET"}[operation]

# After
match operation:
    case "create":
        result = "POST"
    case "read":
        result = "GET"
    case _matchify_key:
        raise KeyError(_matchify_key)

Development

Development and repository-testing notes are in CONTRIBUTING.md.

Issues

If you encounter any problems, please report an issue along with a detailed description.

License

Distributed under the terms of the MIT license, "matchify" is free and open source software.