use_fstring.py

import libcst as cst
import libcst.matchers as m
from fixit import CstLintRule
from fixit import InvalidTestCase as Invalid
from fixit import ValidTestCase as Valid


class UseFstringRule(CstLintRule):
    MESSAGE: str = (
        "As mentioned in the [Contributing Guidelines]"
        "(https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md), "
        "please do not use printf style formatting or `str.format()`. "
        "Use [f-string](https://realpython.com/python-f-strings/) instead to be "
        "more readable and efficient."
    )

    VALID = [
        Valid("assigned='string'; f'testing {assigned}'"),
        Valid("'simple string'"),
        Valid("'concatenated' + 'string'"),
        Valid("b'bytes %s' % 'string'.encode('utf-8')"),
    ]

    INVALID = [
        Invalid("'hello, {name}'.format(name='you')"),
        Invalid("'hello, %s' % 'you'"),
        Invalid("r'raw string value=%s' % val"),
    ]

    def visit_Call(self, node: cst.Call) -> None:
        if m.matches(
            node,
            m.Call(
                func=m.Attribute(value=m.SimpleString(), attr=m.Name(value="format"))
            ),
        ):
            self.report(node)

    def visit_BinaryOperation(self, node: cst.BinaryOperation) -> None:
        if (
            m.matches(
                node, m.BinaryOperation(left=m.SimpleString(), operator=m.Modulo())
            )
            # SimpleString can be bytes and fstring don't support bytes.
            # https://www.python.org/dev/peps/pep-0498/#no-binary-f-strings
            and isinstance(
                cst.ensure_type(node.left, cst.SimpleString).evaluated_value, str
            )
        ):
            self.report(node)