Change rule to "r" last

docs/the_black_code_style/current_style.md

@@ -235,10 +235,10 @@ escapes than before.
 
 _Black_ also standardizes string prefixes. Prefix characters are made lowercase with the
 exception of [capital "R" prefixes](#rstrings-and-rstrings), and in the case of multiple
-characters "r" is put first as in spoken language: "raw f-string". On top of that, if
-your code is already Python 3.6+ only or it's using the `unicode_literals` future
-import, _Black_ will remove `u` from the string prefix as it is meaningless in those
-scenarios.
+characters "r" is put last as the common prefix and as required in Python 2. On top of
+that, if your code is already Python 3.6+ only or it's using the `unicode_literals`
+future import, _Black_ will remove `u` from the string prefix as it is meaningless in
+those scenarios.
 
 The main reason to standardize on a single form of quotes is aesthetics. Having one kind
 of quotes everywhere reduces reader distraction. It will also enable a future version of

src/black/strings.py

@@ -151,7 +151,7 @@ def normalize_string_prefix(s: str) -> str:
     )
 
     # Python syntax guarantees max 2 prefixes and that one of them is "r"
-    if len(new_prefix) == 2 and "r" != new_prefix[0].lower():
+    if len(new_prefix) == 2 and "r" == new_prefix[0].lower():
         new_prefix = new_prefix[::-1]
     return f"{new_prefix}{match.group(2)}"
 
@@ -188,9 +188,9 @@ def normalize_string_quotes(s: str) -> str:
         return s  # There's an internal error
 
     prefix = s[:first_quote_pos]
-    unescaped_new_quote = _cached_compile(rf"(([^\\]|^)(\\\\)*){new_quote}")
-    escaped_new_quote = _cached_compile(rf"([^\\]|^)\\((?:\\\\)*){new_quote}")
-    escaped_orig_quote = _cached_compile(rf"([^\\]|^)\\((?:\\\\)*){orig_quote}")
+    unescaped_new_quote = _cached_compile(fr"(([^\\]|^)(\\\\)*){new_quote}")
+    escaped_new_quote = _cached_compile(fr"([^\\]|^)\\((?:\\\\)*){new_quote}")
+    escaped_orig_quote = _cached_compile(fr"([^\\]|^)\\((?:\\\\)*){orig_quote}")
     body = s[first_quote_pos + len(orig_quote) : -len(orig_quote)]
     if "r" in prefix.casefold():
         if unescaped_new_quote.search(body):
@@ -202,13 +202,13 @@ def normalize_string_quotes(s: str) -> str:
         new_body = body
     else:
         # remove unnecessary escapes
-        new_body = sub_twice(escaped_new_quote, rf"\1\2{new_quote}", body)
+        new_body = sub_twice(escaped_new_quote, fr"\1\2{new_quote}", body)
         if body != new_body:
             # Consider the string without unnecessary escapes as the original
             body = new_body
             s = f"{prefix}{orig_quote}{body}{orig_quote}"
-        new_body = sub_twice(escaped_orig_quote, rf"\1\2{orig_quote}", new_body)
-        new_body = sub_twice(unescaped_new_quote, rf"\1\\{new_quote}", new_body)
+        new_body = sub_twice(escaped_orig_quote, fr"\1\2{orig_quote}", new_body)
+        new_body = sub_twice(unescaped_new_quote, fr"\1\\{new_quote}", new_body)
     if "f" in prefix.casefold():
         matches = re.findall(
             r"""

src/blib2to3/pgen2/tokenize.py

@@ -293,7 +293,7 @@ def compat(self, token: Tuple[int, Text], iterable: Iterable[TokenInfo]) -> None
 
 
 cookie_re = re.compile(r"^[ \t\f]*#.*?coding[:=][ \t]*([-\w.]+)", re.ASCII)
-blank_re = re.compile(rb"^[ \t\f]*(?:[#\r\n]|$)", re.ASCII)
+blank_re = re.compile(br"^[ \t\f]*(?:[#\r\n]|$)", re.ASCII)
 
 
 def _get_normal_name(orig_enc: str) -> str:

tests/data/string_prefixes.py

@@ -31,8 +31,8 @@ def docstring_multiline():
 ("", "")
 (r"", R"")
 
-(rf"", rf"", Rf"", Rf"", rf"", rf"", Rf"", Rf"")
-(rb"", rb"", Rb"", Rb"", rb"", rb"", Rb"", Rb"")
+(fr"", fr"", fR"", fR"", fr"", fr"", fR"", fR"")
+(br"", br"", bR"", bR"", br"", br"", bR"", bR"")
 
 
 def docstring_singleline():

tests/data/string_quotes.py

@@ -23,7 +23,7 @@
 r'Date d\'expiration:(.*)'
 r'Tricky "quote'
 r'Not-so-tricky \"quote'
-rf'{yay}'
+fr'{yay}'
 '\n\
 The \"quick\"\n\
 brown fox\n\
@@ -83,7 +83,7 @@
 r"Date d\'expiration:(.*)"
 r'Tricky "quote'
 r"Not-so-tricky \"quote"
-rf"{yay}"
+fr"{yay}"
 "\nThe \"quick\"\nbrown fox\njumps over\nthe 'lazy' dog.\n"
 re.compile(r'[\\"]')
 "x = ''; y = \"\""

tests/test_black.py

@@ -290,7 +290,7 @@ def test_expression_diff(self) -> None:
         expected, _ = read_data("expression.diff")
         tmp_file = Path(black.dump_to_file(source))
         diff_header = re.compile(
-            rf"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
+            fr"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
             r"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"
         )
         try:
@@ -355,7 +355,7 @@ def test_skip_magic_trailing_comma(self) -> None:
         expected, _ = read_data("expression_skip_magic_trailing_comma.diff")
         tmp_file = Path(black.dump_to_file(source))
         diff_header = re.compile(
-            rf"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
+            fr"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
             r"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"
         )
         try:
@@ -1424,7 +1424,7 @@ def test_bpo_2142_workaround(self) -> None:
         expected, _ = read_data("missing_final_newline.diff")
         tmp_file = Path(black.dump_to_file(source, ensure_final_newline=False))
         diff_header = re.compile(
-            rf"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
+            fr"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
             r"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"
         )
         try:

tests/test_ipynb.py

@@ -341,7 +341,7 @@ def test_empty_string() -> None:
 
 def test_unparseable_notebook() -> None:
     path = DATA_DIR / "notebook_which_cant_be_parsed.ipynb"
-    msg = rf"File '{re.escape(str(path))}' cannot be parsed as valid Jupyter notebook\."
+    msg = fr"File '{re.escape(str(path))}' cannot be parsed as valid Jupyter notebook\."
     with pytest.raises(ValueError, match=msg):
         format_file_in_place(path, fast=True, mode=JUPYTER_MODE)