Invert `getattr()` check for `get_mkt_pairs()` ep

Such that we `return` early when not defined by the provider backend to
reduce an indent level in `SymbologyCache.load()`.

piker/data/_symcache.py

@@ -31,6 +31,7 @@ from pathlib import Path
 from pprint import pformat
 from typing import (
     Any,
+    Callable,
     Sequence,
     Hashable,
     TYPE_CHECKING,
@@ -56,7 +57,7 @@ from piker.brokers import (
 )
 
 if TYPE_CHECKING:
-    from ..accounting import (
+    from piker.accounting import (
         Asset,
         MktPair,
     )
@@ -149,57 +150,68 @@ class SymbologyCache(Struct):
                     'Implement `Client.get_assets()`!'
                 )
 
-            if get_mkt_pairs := getattr(client, 'get_mkt_pairs', None):
-
-                pairs: dict[str, Struct] = await get_mkt_pairs()
-                for bs_fqme, pair in pairs.items():
-
-                    # NOTE: every backend defined pair should
-                    # declare it's ns path for roundtrip
-                    # serialization lookup.
-                    if not getattr(pair, 'ns_path', None):
-                        raise TypeError(
-                            f'Pair-struct for {self.mod.name} MUST define a '
-                            '`.ns_path: str`!\n'
-                            f'{pair}'
-                        )
-
-                    entry = await self.mod.get_mkt_info(pair.bs_fqme)
-                    if not entry:
-                        continue
-
-                    mkt: MktPair
-                    pair: Struct
-                    mkt, _pair = entry
-                    assert _pair is pair, (
-                        f'`{self.mod.name}` backend probably has a '
-                        'keying-symmetry problem between the pair-`Struct` '
-                        'returned from `Client.get_mkt_pairs()`and the '
-                        'module level endpoint: `.get_mkt_info()`\n\n'
-                        "Here's the struct diff:\n"
-                        f'{_pair - pair}'
-                    )
-                    # NOTE XXX: this means backends MUST implement
-                    # a `Struct.bs_mktid: str` field to provide
-                    # a native-keyed map to their own symbol
-                    # set(s).
-                    self.pairs[pair.bs_mktid] = pair
-
-                    # NOTE: `MktPair`s are keyed here using piker's
-                    # internal FQME schema so that search,
-                    # accounting and feed init can be accomplished
-                    # a sane, uniform, normalized basis.
-                    self.mktmaps[mkt.fqme] = mkt
-
-                self.pair_ns_path: str = tractor.msg.NamespacePath.from_ref(
-                    pair,
-                )
-
-            else:
+            get_mkt_pairs: Callable|None = getattr(
+                client,
+                'get_mkt_pairs',
+                None,
+            )
+            if not get_mkt_pairs:
                 log.warning(
                     'No symbology cache `Pair` support for `{provider}`..\n'
                     'Implement `Client.get_mkt_pairs()`!'
                 )
+                return self
+
+            pairs: dict[str, Struct] = await get_mkt_pairs()
+            if not pairs:
+                log.warning(
+                    'No pairs from intial {provider!r} sym-cache request?\n\n'
+                    '`Client.get_mkt_pairs()` -> {pairs!r} ?'
+                )
+                return self
+
+            for bs_fqme, pair in pairs.items():
+                if not getattr(pair, 'ns_path', None):
+                    # XXX: every backend defined pair must declare
+                    # a `.ns_path: tractor.NamespacePath` to enable
+                    # roundtrip serialization lookup from a local
+                    # cache file.
+                    raise TypeError(
+                        f'Pair-struct for {self.mod.name} MUST define a '
+                        '`.ns_path: str`!\n\n'
+                        f'{pair!r}'
+                    )
+
+                entry = await self.mod.get_mkt_info(pair.bs_fqme)
+                if not entry:
+                    continue
+
+                mkt: MktPair
+                pair: Struct
+                mkt, _pair = entry
+                assert _pair is pair, (
+                    f'`{self.mod.name}` backend probably has a '
+                    'keying-symmetry problem between the pair-`Struct` '
+                    'returned from `Client.get_mkt_pairs()`and the '
+                    'module level endpoint: `.get_mkt_info()`\n\n'
+                    "Here's the struct diff:\n"
+                    f'{_pair - pair}'
+                )
+                # NOTE XXX: this means backends MUST implement
+                # a `Struct.bs_mktid: str` field to provide
+                # a native-keyed map to their own symbol
+                # set(s).
+                self.pairs[pair.bs_mktid] = pair
+
+                # NOTE: `MktPair`s are keyed here using piker's
+                # internal FQME schema so that search,
+                # accounting and feed init can be accomplished
+                # a sane, uniform, normalized basis.
+                self.mktmaps[mkt.fqme] = mkt
+
+            self.pair_ns_path: str = tractor.msg.NamespacePath.from_ref(
+                pair,
+            )
 
         return self