qt history: speed up ensure_fields_available (faster startup)

electrum/util.py

@@ -22,7 +22,7 @@
 # SOFTWARE.
 import binascii
 import os, sys, re, json
-from collections import defaultdict
+from collections import defaultdict, OrderedDict
 from typing import NamedTuple, Union, TYPE_CHECKING, Tuple, Optional, Callable
 from datetime import datetime
 import decimal
@@ -993,3 +993,55 @@ def create_and_start_event_loop() -> Tuple[asyncio.AbstractEventLoop,
                                          name='EventLoop')
     loop_thread.start()
     return loop, stopping_fut, loop_thread
+
+
+class OrderedDictWithIndex(OrderedDict):
+    """An OrderedDict that keeps track of the positions of keys.
+
+    Note: very inefficient to modify contents, except to add new items.
+    """
+
+    _key_to_pos = {}
+
+    def _recalc_key_to_pos(self):
+        self._key_to_pos = {key: pos for (pos, key) in enumerate(self.keys())}
+
+    def get_pos_of_key(self, key):
+        return self._key_to_pos[key]
+
+    def popitem(self, *args, **kwargs):
+        ret = super().popitem(*args, **kwargs)
+        self._recalc_key_to_pos()
+        return ret
+
+    def move_to_end(self, *args, **kwargs):
+        ret = super().move_to_end(*args, **kwargs)
+        self._recalc_key_to_pos()
+        return ret
+
+    def clear(self):
+        ret = super().clear()
+        self._recalc_key_to_pos()
+        return ret
+
+    def pop(self, *args, **kwargs):
+        ret = super().pop(*args, **kwargs)
+        self._recalc_key_to_pos()
+        return ret
+
+    def update(self, *args, **kwargs):
+        ret = super().update(*args, **kwargs)
+        self._recalc_key_to_pos()
+        return ret
+
+    def __delitem__(self, *args, **kwargs):
+        ret = super().__delitem__(*args, **kwargs)
+        self._recalc_key_to_pos()
+        return ret
+
+    def __setitem__(self, key, *args, **kwargs):
+        is_new_key = key not in self
+        ret = super().__setitem__(key, *args, **kwargs)
+        if is_new_key:
+            self._key_to_pos[key] = len(self) - 1
+        return ret