Added the fstring grammar without the tokenization part

This means that fstrings are not yet parsed, because there are no f-string tokens.

parso/python/errors.py

@@ -563,7 +563,8 @@ class _ReturnAndYieldChecks(SyntaxRule):
                     and self._normalizer.version == (3, 5):
                 self.add_issue(self.get_node(leaf), message=self.message_async_yield)
 
-@ErrorFinder.register_rule(type='atom')
+
+@ErrorFinder.register_rule(type='strings')
 class _BytesAndStringMix(SyntaxRule):
     # e.g. 's' b''
     message = "cannot mix bytes and nonbytes literals"
@@ -949,7 +950,7 @@ class _CheckAssignmentRule(SyntaxRule):
             first, second = node.children[:2]
             error = _get_comprehension_type(node)
             if error is None:
-                if second.type in ('dictorsetmaker', 'string'):
+                if second.type == 'dictorsetmaker':
                     error = 'literal'
                 elif first in ('(', '['):
                     if second.type == 'yield_expr':
@@ -968,7 +969,7 @@ class _CheckAssignmentRule(SyntaxRule):
                 error = 'Ellipsis'
         elif type_ == 'comparison':
             error = 'comparison'
-        elif type_ in ('string', 'number'):
+        elif type_ in ('string', 'number', 'strings'):
             error = 'literal'
         elif type_ == 'yield_expr':
             # This one seems to be a slightly different warning in Python.

parso/python/grammar36.txt

@@ -108,7 +108,7 @@ 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')
 testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']
@@ -148,3 +148,9 @@ encoding_decl: NAME
 
 yield_expr: 'yield' [yield_arg]
 yield_arg: 'from' test | testlist
+
+strings: (STRING | fstring)+
+fstring: FSTRING_START fstring_content FSTRING_END
+fstring_content: (FSTRING_STRING | fstring_expr)*
+fstring_expr: '{' testlist  [ FSTRING_CONVERSION ] [ fstring_format_spec ] '}'
+fstring_format_spec: ':' fstring_content

parso/python/token.py

@@ -32,6 +32,14 @@ if py_version < 35:
 ERROR_DEDENT = next(_counter)
 tok_name[ERROR_DEDENT] = 'ERROR_DEDENT'
 
+FSTRING_START = next(_counter)
+tok_name[FSTRING_START] = 'FSTRING_START'
+FSTRING_END = next(_counter)
+tok_name[FSTRING_END] = 'FSTRING_END'
+FSTRING_STRING = next(_counter)
+tok_name[FSTRING_STRING] = 'FSTRING_STRING'
+FSTRING_CONVERSION = next(_counter)
+tok_name[FSTRING_CONVERSION] = 'FSTRING_CONVERSION'
 
 # Map from operator to number (since tokenize doesn't do this)
 

parso/python/tokenize.py

@@ -25,6 +25,13 @@ from parso._compatibility import py_version
 from parso.utils import split_lines
 
 
+#fstring_start = /[f|fr|rf]["|"""|'|''']/
+#fstring_end = <same as the second part of the fstring start>
+fstring_expr_start = ''
+fstring_string = r'([^{}\n]+|\{\{|\}\})*'
+fstring_conversion = r'![sra]'
+
+
 TokenCollection = namedtuple(
     'TokenCollection',
     'pseudo_token single_quoted triple_quoted endpats always_break_tokens',