1# This file is part of the lib3to6 project 

2# https://github.com/mbarkhau/lib3to6 

3# 

4# Copyright (c) 2019-2021 Manuel Barkhau (mbarkhau@gmail.com) - MIT License 

5# SPDX-License-Identifier: MIT 

6 

7import ast 

8import typing as typ 

9 

10from . import common 

11from . import fixer_base as fb 

12 

13 

14class FStringToStrFormatFixer(fb.TransformerFixerBase): 

15 

16 version_info = common.VersionInfo(apply_since="2.6", apply_until="3.5") 

17 

18 def _formatted_value_str( 

19 self, fmt_val_node: ast.FormattedValue, arg_nodes: typ.List[ast.expr] 

20 ) -> str: 

21 arg_index = len(arg_nodes) 

22 arg_nodes.append(fmt_val_node.value) 

23 

24 format_spec_node = fmt_val_node.format_spec 

25 if format_spec_node is None: 

26 format_spec = "" 

27 elif not isinstance(format_spec_node, ast.JoinedStr): 

28 raise common.FixerError("Unexpected Node Type", format_spec_node) 

29 else: 

30 format_spec = ":" + self._joined_str_str(format_spec_node, arg_nodes) 

31 

32 return "{" + str(arg_index) + format_spec + "}" 

33 

34 def _joined_str_str(self, joined_str_node: ast.JoinedStr, arg_nodes: typ.List[ast.expr]) -> str: 

35 fmt_str = "" 

36 for val in joined_str_node.values: 

37 if isinstance(val, ast.Str): 

38 fmt_str += val.s 

39 elif isinstance(val, ast.FormattedValue): 

40 fmt_str += self._formatted_value_str(val, arg_nodes) 

41 else: 

42 raise common.FixerError("Unexpected Node Type", val) 

43 return fmt_str 

44 

45 def visit_JoinedStr(self, node: ast.JoinedStr) -> ast.Call: 

46 arg_nodes: typ.List[ast.expr] = [] 

47 

48 fmt_str = self._joined_str_str(node, arg_nodes) 

49 format_attr_node = ast.Attribute(value=ast.Str(s=fmt_str), attr="format", ctx=ast.Load()) 

50 return ast.Call(func=format_attr_node, args=arg_nodes, keywords=[])