adding arrow functions to Python grammar

arrowfunc.patch

diff --git a/Grammar/Tokens b/Grammar/Tokens
index 618ae81..29bcfeb 100644
--- a/Grammar/Tokens
+++ b/Grammar/Tokens
@@ -11,6 +11,7 @@ RPAR                    ')'
 LSQB                    '['
 RSQB                    ']'
 COLON                   ':'
+FUNC_SIGN               '=>'
 COMMA                   ','
 SEMI                    ';'
 PLUS                    '+'
diff --git a/Grammar/python.gram b/Grammar/python.gram
index c1863ae..337a6d0 100644
--- a/Grammar/python.gram
+++ b/Grammar/python.gram
@@ -674,6 +674,7 @@ expressions[expr_ty]:
 expression[expr_ty] (memo):
     | invalid_expression
     | invalid_legacy_expression
+    | lambarrowdef
     | a=disjunction 'if' b=disjunction 'else' c=expression { _PyAST_IfExp(b, a, c, EXTRA) }
     | disjunction
     | lambdef
@@ -858,6 +859,9 @@ group[expr_ty]:
 lambdef[expr_ty]:
     | 'lambda' a=[lambda_params] ':' b=expression {
         _PyAST_Lambda((a) ? a : CHECK(arguments_ty, _PyPegen_empty_arguments(p)), b, EXTRA) }
+lambarrowdef[expr_ty]:
+    | '(' a=[params] ')' '=>' b=expression {
+        _PyAST_Lambda((a) ? a : CHECK(arguments_ty, _PyPegen_empty_arguments(p)), b, EXTRA) }
 
 lambda_params[arguments_ty]:
     | invalid_lambda_parameters

Thank you very much! Nice work. 🔥🤝