Gracefully handle pickle-errors when @staticmethod is used

pOinted out in https://github.com/freqtrade/freqtrade-strategies/issues/28

freqtrade/resolvers/strategy_resolver.py

@@ -157,12 +157,15 @@ class StrategyResolver(IResolver):
                         getfullargspec(strategy.populate_indicators).args)
                     strategy._buy_fun_len = len(getfullargspec(strategy.populate_buy_trend).args)
                     strategy._sell_fun_len = len(getfullargspec(strategy.populate_sell_trend).args)
-
+                    try:
                         return import_strategy(strategy, config=config)
+                    except TypeError as e:
+                        logger.warning(
+                            f"Impossible to load strategy '{strategy}' from {_path}. Error: {e}")
             except FileNotFoundError:
                 logger.warning('Path "%s" does not exist', _path.relative_to(Path.cwd()))
 
         raise ImportError(
-            "Impossible to load Strategy '{}'. This class does not exist"
-            " or contains Python code errors".format(strategy_name)
+            f"Impossible to load Strategy '{strategy_name}'. This class does not exist"
+            " or contains Python code errors"
         )

freqtrade/tests/strategy/test_strategy.py

@@ -1,17 +1,19 @@
 # pragma pylint: disable=missing-docstring, protected-access, C0103
 import logging
+import warnings
 from base64 import urlsafe_b64encode
 from os import path
 from pathlib import Path
-import warnings
+from unittest.mock import Mock
 
 import pytest
 from pandas import DataFrame
 
+from freqtrade.resolvers import StrategyResolver
 from freqtrade.strategy import import_strategy
 from freqtrade.strategy.default_strategy import DefaultStrategy
 from freqtrade.strategy.interface import IStrategy
-from freqtrade.resolvers import StrategyResolver
+from freqtrade.tests.conftest import log_has_re
 
 
 def test_import_strategy(caplog):
@@ -94,6 +96,16 @@ def test_load_not_found_strategy():
         strategy._load_strategy(strategy_name='NotFoundStrategy', config={})
 
 
+def test_load_staticmethod_importerror(mocker, caplog):
+    mocker.patch("freqtrade.resolvers.strategy_resolver.import_strategy", Mock(
+        side_effect=TypeError("can't pickle staticmethod objects")))
+    with pytest.raises(ImportError,
+                       match=r"Impossible to load Strategy 'DefaultStrategy'."
+                             r" This class does not exist or contains Python code errors"):
+        StrategyResolver()
+    assert log_has_re(r".*Error: can't pickle staticmethod objects", caplog.record_tuples)
+
+
 def test_strategy(result):
     config = {'strategy': 'DefaultStrategy'}