def union_many(self, others):
        """
        A bit of a hack to accelerate unioning a collection of indexes
        """
        this = self

        for other in others:
            if not isinstance(this, DatetimeIndex):
                this = Index.union(this, other)
                continue

            if not isinstance(other, DatetimeIndex):
                try:
                    other = DatetimeIndex(other)
                except __HOLE__:
                    pass

            this, other = this._maybe_utc_convert(other)

            if this._can_fast_union(other):
                this = this._fast_union(other)
            else:
                tz = this.tz
                this = Index.union(this, other)
                if isinstance(this, DatetimeIndex):
                    this.tz = tz

        if this.freq is None:
            this.offset = to_offset(this.inferred_freq)
        return this
dataset/ETHPy150Open pydata/pandas/pandas/tseries/index.py/DatetimeIndex.union_many