add str.isascii

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/str/StringBuiltins.java

@@ -54,6 +54,7 @@
 import java.nio.CharBuffer;
 import java.nio.charset.CharacterCodingException;
 import java.nio.charset.Charset;
+import java.nio.charset.CharsetEncoder;
 import java.nio.charset.CodingErrorAction;
 import java.nio.charset.IllegalCharsetNameException;
 import java.nio.charset.UnsupportedCharsetException;
@@ -1606,6 +1607,19 @@ Object doGeneric(VirtualFrame frame, String left, Object right,
         }
     }
 
+    @Builtin(name = "isascii", minNumOfPositionalArgs = 1)
+    @GenerateNodeFactory
+    @TypeSystemReference(PythonArithmeticTypes.class)
+    abstract static class IsAsciiNode extends PythonUnaryBuiltinNode {
+        private static final CharsetEncoder asciiEncoder = Charset.forName("US-ASCII").newEncoder();
+
+        @Specialization
+        @TruffleBoundary
+        boolean doString(String self) {
+            return asciiEncoder.canEncode(self);
+        }
+    }
+
     @Builtin(name = "isalnum", minNumOfPositionalArgs = 1)
     @GenerateNodeFactory
     @TypeSystemReference(PythonArithmeticTypes.class)