Merge pull request #2 from zapier/single-quote-option-triples

Keep using double quotes for triple-quoted strings with --single-quote.

README.md

@@ -69,7 +69,7 @@ black [OPTIONS] [SRC]...
 Options:
   -l, --line-length INTEGER   Where to wrap around.  [default: 88]
   --single-quote              Use single quotes instead of double quotes in
-                              strings.
+                              strings except for triple-quoted strings.
   --check                     Don't write the files back, just return the
                               status.  Return code 0 means nothing would
                               change.  Return code 1 means some files would be

black.py

@@ -2338,17 +2338,19 @@ def normalize_string_quotes(leaf: Leaf, single_quote: bool = False) -> None:
 
     quote_char = '"'
     alt_quote_char = "'"
+    triple_quote_chars = '"""'
+    alt_triple_quote_chars = "'''"
 
     if single_quote:
         quote_char = "'"
         alt_quote_char = '"'
 
-    if value[:3] == (quote_char * 3):
+    if value[:3] == triple_quote_chars:
         return
 
-    elif value[:3] == (alt_quote_char * 3):
-        orig_quote = alt_quote_char * 3
-        new_quote = quote_char * 3
+    elif value[:3] == alt_triple_quote_chars:
+        orig_quote = alt_triple_quote_chars
+        new_quote = triple_quote_chars
     elif value[0] == quote_char:
         orig_quote = quote_char
         new_quote = alt_quote_char
@@ -2381,9 +2383,9 @@ def normalize_string_quotes(leaf: Leaf, single_quote: bool = False) -> None:
             leaf.value = 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)
-    if new_quote == (quote_char * 3) and new_body[-1] == quote_char:
+    if new_quote == triple_quote_chars and new_body[-1] == triple_quote_chars[0]:
         # edge case:
-        new_body = new_body[:-1] + "\\" + quote_char
+        new_body = new_body[:-1] + "\\" + triple_quote_chars[0]
     orig_escape_count = body.count("\\")
     new_escape_count = new_body.count("\\")
     if new_escape_count > orig_escape_count: