MNT: Adapt for pandas 1.0.0 (bug workaround + two depr warnings)

backtesting/_util.py

@@ -33,10 +33,7 @@ def _as_list(value):
 
 def _data_period(df):
     """Return data index period as pd.Timedelta"""
-    if df.index.is_all_dates:
-        values = df.index[:100].to_series(keep_tz=True)
-    else:
-        values = df.index[:100].to_series()
+    values = df.index[-100:].to_series()
     return values.diff().median()
 
 

backtesting/backtesting.py

@@ -896,7 +896,7 @@ class Backtest:
             resolution = getattr(_period, 'resolution_string', None) or _period.resolution
             return value.ceil(resolution)
 
-        s = pd.Series()
+        s = pd.Series(dtype=object)
         s.loc['Start'] = df.index[0]
         s.loc['End'] = df.index[-1]
         s.loc['Duration'] = s.End - s.Start

backtesting/lib.py

@@ -209,6 +209,7 @@ def resample_apply(rule: str,
             'or a `Strategy.data.*` array'
         series = series.to_series()
 
+    series = series.copy()  # XXX: pandas 1.0.1 bug https://github.com/pandas-dev/pandas/issues/31710
     resampled = series.resample(rule, label='right').agg(agg).dropna()
     resampled.name = _as_str(series) + '[' + rule + ']'