Compute symbol digits at creation time

Add a new factory func `mk_symbol()` to create the initial
instance at feed creation time.

piker/data/_source.py

@@ -62,6 +62,9 @@ tf_in_1m = {
 def float_digits(
     value: float,
 ) -> int:
+    if value == 0:
+        return 0
+
     return int(-decimal.Decimal(str(value)).as_tuple().exponent)
 
 
@@ -82,28 +85,20 @@ class Symbol(BaseModel):
     Yah, i guess dats what it izz.
     """
     key: str
-    tick_size: float = 0.01
-    lot_tick_size: float = 0.01  # "volume" precision as min step value
+    type_key: str  # {'stock', 'forex', 'future', ... etc.}
+    tick_size: float
+    lot_tick_size: float  # "volume" precision as min step value
+    tick_size_digits: int
+    lot_size_digits: int
     broker_info: Dict[str, Dict[str, Any]] = {}
 
     # specifies a "class" of financial instrument
     # ex. stock, futer, option, bond etc.
-    type_key: str
 
     @property
     def brokers(self) -> List[str]:
         return list(self.broker_info.keys())
 
-    def digits(self) -> int:
-        """Return the trailing number of digits specified by the min
-        tick size for the instrument.
-
-        """
-        return float_digits(self.tick_size)
-
-    def lot_digits(self) -> int:
-        return float_digits(self.lot_tick_size)
-
     def nearest_tick(self, value: float) -> float:
         """Return the nearest tick value based on mininum increment.
 
@@ -112,6 +107,30 @@ class Symbol(BaseModel):
         return round(value * mult) / mult
 
 
+def mk_symbol(
+
+    key: str,
+    type_key: str,
+    tick_size: float = 0.01,
+    lot_tick_size: float = 0,
+    broker_info: dict[str, Any] = {},
+
+) -> Symbol:
+    '''Create and return an instrument description for the
+    "symbol" named as ``key``.
+
+    '''
+    return Symbol(
+        key=key,
+        type_key=type_key,
+        tick_size=tick_size,
+        lot_tick_size=lot_tick_size,
+        tick_size_digits=float_digits(tick_size),
+        lot_size_digits=float_digits(lot_tick_size),
+        broker_info=broker_info,
+    )
+
+
 def from_df(
     df: pd.DataFrame,
     source=None,

piker/data/feed.py

@@ -49,7 +49,7 @@ from ._sharedmem import (
     ShmArray,
 )
 from .ingest import get_ingestormod
-from ._source import base_iohlc_dtype, Symbol
+from ._source import base_iohlc_dtype, mk_symbol, Symbol
 from ..ui import _search
 from ._sampling import (
     _shms,
@@ -535,7 +535,7 @@ async def open_feed(
             si = data['symbol_info']
             ohlc_sample_rates.append(data['sample_rate'])
 
-            symbol = Symbol(
+            symbol = mk_symbol(
                 key=sym,
                 type_key=si.get('asset_type', 'forex'),
                 tick_size=si.get('price_tick_size', 0.01),

piker/ui/_chart.py

@@ -371,7 +371,7 @@ class LinkedSplits(QWidget):
         # add crosshairs
         self.cursor = Cursor(
             linkedsplits=self,
-            digits=symbol.digits(),
+            digits=symbol.tick_size_digits,
         )
 
         self.chart = self.add_plot(
@@ -882,7 +882,7 @@ class ChartPlotWidget(pg.PlotWidget):
         # use the tick size precision for display
         sym = self.linked.symbol
         if name == sym.key:
-            digits = sym.digits()
+            digits = sym.tick_size_digits
         else:
             digits = 2
 
@@ -1144,8 +1144,8 @@ async def chart_from_quotes(
     l1 = L1Labels(
         chart,
         # determine precision/decimal lengths
-        digits=symbol.digits(),
-        size_digits=symbol.lot_digits(),
+        digits=symbol.tick_size_digits,
+        size_digits=symbol.lot_size_digits,
     )
     chart._l1_labels = l1
 

piker/ui/_position.py

@@ -169,7 +169,7 @@ def mk_alloc(
             '''
             tracker = self._position
             pp_size = tracker.live_pp.size
-            ld = symbol.lot_digits()
+            ld = symbol.lot_size_digits
 
             if (
                 action == 'buy' and pp_size > 0 or
@@ -289,7 +289,7 @@ class PositionTracker:
         )
         pp_label.render()
 
-        nsize = self.chart.linked.symbol.lot_digits()
+        nsize = self.chart.linked.symbol.lot_size_digits
 
         self.size_label = size_label = Label(
             view=view,

piker/ui/order_mode.py

@@ -116,12 +116,9 @@ class OrderMode:
             # TODO: convert these values into human-readable form
             # (i.e. with k, m, M, B) type embedded suffixes
             level=order.price,
-            # level_digits=symbol.digits(),
             action=order.action,
 
             size=order.size,
-            # TODO: we need truncation checks in the EMS for this?
-            # size_digits=min(symbol.lot_digits(), 3),
             color=self._colors[order.action],
 
             dotted=True if (