class_docstr: Not sure if I can avoid the state machine here
class_docstr_tok: ["Not","sure","if","I","can","avoid","the","state","machine","here"]
code: def _get_monthly_rule(self):
      if len(self.mdiffs) > 1:
          return None
      pos_check = self.month_position_check()
      return {"cs": "MS", "bs": "BMS", "ce": "M", "be": "BM"}.get(
          pos_check
      )
  
imports: from datetime import timedelta
  import re
  import numpy
  from pytz import AmbiguousTimeError
  from pandas._libs.algos import unique_deltas
  from pandas._libs.tslibs import Timedelta, Timestamp
  from pandas._libs.tslibs.ccalendar import MONTH_ALIASES, int_to_weekday
  from pandas._libs.tslibs.conversion import tz_convert
  from pandas._libs.tslibs.fields import build_field_sarray
  import pandas._libs.tslibs.frequencies
  from pandas._libs.tslibs.offsets import _offset_to_period_map
  import pandas._libs.tslibs.resolution
  from pandas._libs.tslibs.resolution import Resolution
  from pandas._libs.tslibs.timezones import UTC
  import pandas.compat
  from pandas.compat import zip
  from pandas.util._decorators import cache_readonly
  from pandas.core.dtypes.common import is_datetime64_dtype, is_period_arraylike, is_timedelta64_dtype
  from pandas.core.dtypes.generic import ABCSeries
  from pandas.core.algorithms import unique
  from pandas.tseries.offsets import DateOffset, Day, Hour, Micro, Milli, Minute, Nano, Second, prefix_mapping
label_desc: Use image node_id 17 for calling the _FrequencyInferer obj's underlying member method code with example usage: obj._get_monthly_rule() and returns: dict, None