Use strings as a non-terminal symbol in all grammars

This makes it easier to write the same logic for all Python versions

parso/python/grammar26.txt

@@ -119,7 +119,8 @@ atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [listmaker] ']' |
        '{' [dictorsetmaker] '}' |
        '`' testlist1 '`' |
-       NAME | NUMBER | STRING+)
+       NAME | NUMBER | strings)
+strings: STRING+
 listmaker: test ( list_for | (',' test)* [','] )
 # Dave: Renamed testlist_gexpr to testlist_comp, because in 2.7+ this is the
 #       default. It's more consistent like this.

parso/python/grammar27.txt

@@ -104,7 +104,8 @@ atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [listmaker] ']' |
        '{' [dictorsetmaker] '}' |
        '`' testlist1 '`' |
-       NAME | NUMBER | STRING+)
+       NAME | NUMBER | strings)
+strings: STRING+
 listmaker: test ( list_for | (',' test)* [','] )
 testlist_comp: test ( comp_for | (',' test)* [','] )
 lambdef: 'lambda' [varargslist] ':' test

parso/python/grammar33.txt

@@ -103,7 +103,8 @@ power: atom trailer* ['**' factor]
 atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [testlist_comp] ']' |
        '{' [dictorsetmaker] '}' |
-       NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')
+       NAME | NUMBER | strings | '...' | 'None' | 'True' | 'False')
+strings: STRING+
 testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']

parso/python/grammar34.txt

@@ -103,7 +103,8 @@ power: atom trailer* ['**' factor]
 atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [testlist_comp] ']' |
        '{' [dictorsetmaker] '}' |
-       NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')
+       NAME | NUMBER | strings | '...' | 'None' | 'True' | 'False')
+strings: STRING+
 testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']

parso/python/grammar35.txt

@@ -110,7 +110,8 @@ atom_expr: ['await'] atom trailer*
 atom: ('(' [yield_expr|testlist_comp] ')' |
        '[' [testlist_comp] ']' |
        '{' [dictorsetmaker] '}' |
-       NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')
+       NAME | NUMBER | strings | '...' | 'None' | 'True' | 'False')
+strings: STRING+
 testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']

parso/python/parser.py

@@ -1,6 +1,6 @@
 from parso.python import tree
 from parso.python.token import (DEDENT, INDENT, ENDMARKER, NEWLINE, NUMBER,
-                                STRING, tok_name, NAME)
+                                STRING, tok_name, NAME, FSTRING_STRING)
 from parso.parser import BaseParser
 from parso.pgen2.parse import token_to_ilabel
 
@@ -129,6 +129,8 @@ class Parser(BaseParser):
             return tree.Newline(value, start_pos, prefix)
         elif type == ENDMARKER:
             return tree.EndMarker(value, start_pos, prefix)
+        elif type == FSTRING_STRING:
+            return tree.FStringString(value, start_pos, prefix)
         else:
             return tree.Operator(value, start_pos, prefix)
 

parso/python/tree.py

@@ -262,6 +262,15 @@ class String(Literal):
         return match.group(2)[:-len(match.group(1))]
 
 
+class FStringString(Leaf):
+    """
+    f-strings contain f-string expressions and normal python strings. These are
+    the string parts of f-strings.
+    """
+    type = 'fstring_string'
+    __slots__ = ()
+
+
 class _StringComparisonMixin(object):
     def __eq__(self, other):
         """