format_to_fstring.py

#!/usr/bin/env python3

import argparse
import ast
import astor
import os
import re
import sys


class Interpolator(ast.NodeTransformer):
    def visit_Call(self, node: ast.Call):
        node = self.generic_visit(node)

        is_format_expr = (
            isinstance(node.func, ast.Attribute)
            and node.func.attr == "format"
            and isinstance(node.func.value, ast.Str)
        )

        if not is_format_expr:
            return node

        format_string = node.func.value.s
        format_args = node.args + [None]
        substrings = format_string.split("{}")
        components = []
        for (substring, arg) in zip(substrings, format_args):
            if substring:
                components.append(ast.Str(substring))
            if arg:
                components.append(
                    ast.FormattedValue(arg, conversion=-1, format_spec=None)
                )

        return ast.JoinedStr(components)


def _main():
    parser = argparse.ArgumentParser()
    parser.add_argument("files", nargs="+")
    args = parser.parse_args()

    rewriter = Interpolator()
    for path in args.files:
        with open(path) as input:
            content = input.read()

        rewritten = rewriter.visit(ast.parse(content))

        with open(path, "w") as output:
            output.write(astor.to_source(rewritten))


if __name__ == "__main__":
    _main()