add pin.pin.use_strict() to enable strict pin value getting mode (#241

)

pywebio/pin.py

@@ -135,6 +135,7 @@
 
 def check_name(name):
     assert all(i in _html_value_chars for i in name), "pin `name` can only contain letters, digits and underscore"
+    assert name != 'use_strict', "'use_strict' is a reserve name, can't use as pin widget name"
     assert name[0] in string.ascii_letters, "pin `name` can only starts with letters"
 
 
@@ -224,20 +225,30 @@ def put_actions(name, *, label='', buttons=None, help_text=None,
 
 
 @chose_impl
-def get_client_val():
+def get_client_val(strict=False):
     res = yield next_client_event()
     assert res['event'] == 'js_yield', "Internal Error, please report this bug on " \
                                        "https://github.com/wang0618/PyWebIO/issues"
-    return res['data']
+    data = res['data']
+    assert not strict or data, 'pin widget doesn\'t exist.'
+    return (data or {}).get('value')
 
 
 class Pin_:
+    _strict = False
+
+    def use_strict(self):
+        """
+        Enable strict mode for getting pin widget value.
+        An AssertionError will be raised when try to get value of pin widgets that are currently not in the page.
+        """
+        self._strict = True
 
     def __getattr__(self, name):
         """__getattr__ is only invoked if the attribute wasn't found the usual ways"""
         check_name(name)
         send_msg('pin_value', spec=dict(name=name))
-        return get_client_val()
+        return get_client_val(self._strict)
 
     def __getitem__(self, name):
         return self.__getattr__(name)
@@ -246,6 +257,9 @@ def __setattr__(self, name, value):
         """
         __setattr__ will be invoked regardless of whether the attribute be found
         """
+        if name == '_strict':
+            return object.__setattr__(self, name, value)
+
         check_name(name)
         send_msg('pin_update', spec=dict(name=name, attributes={"value": value}))
 

webiojs/src/handlers/pin.ts

@@ -15,8 +15,9 @@ export class PinHandler implements CommandHandler {
 
     handle_message(msg: Command) {
         if (msg.command === 'pin_value') {
-            let val = GetPinValue(msg.spec.name)
-            state.CurrentSession.send_message({event: "js_yield", task_id: msg.task_id, data: val});
+            let val = GetPinValue(msg.spec.name);
+            let data = val===undefined? null : {value: val};
+            state.CurrentSession.send_message({event: "js_yield", task_id: msg.task_id, data: data});
         } else if (msg.command === 'pin_update') {
             PinUpdate(msg.spec.name, msg.spec.attributes);
         } else if (msg.command === 'pin_wait') {

webiojs/src/models/pin.ts

@@ -7,6 +7,8 @@ import {AfterCurrentOutputWidgetShow} from "../handlers/output";
 let name2input: { [k: string]: InputItem } = {};
 
 export function GetPinValue(name: string) {
+    if(!document.contains(name2input[name].element[0]))
+        return undefined;
     return name2input[name].get_value();
 }