code: def _maybe_convert_index(ax, data):
      # tsplot converts automatically, but don't want to convert index
      # over and over for DataFrames
      if isinstance(data.index, ABCDatetimeIndex):
          freq = getattr(data.index, "freq", None)
  
          if freq is None:
              freq = getattr(data.index, "inferred_freq", None)
          if isinstance(freq, DateOffset):
              freq = freq.rule_code
  
          if freq is None:
              freq = _get_ax_freq(ax)
  
          if freq is None:
              raise ValueError(
                  "Could not get frequency alias for plotting"
              )
  
          freq = get_base_alias(freq)
          freq = frequencies.get_period_alias(freq)
  
          data = data.to_period(freq=freq)
      return data
  
imports: import functools
  from matplotlib import pylab
  import numpy
  from pandas._libs.tslibs.frequencies import FreqGroup, get_base_alias, get_freq, is_subperiod, is_superperiod
  from pandas._libs.tslibs.period import Period
  import pandas.compat
  from pandas.core.dtypes.generic import ABCDatetimeIndex, ABCPeriodIndex, ABCTimedeltaIndex
  from pandas.io.formats.printing import pprint_thing
  from pandas.plotting._converter import TimeSeries_DateFormatter, TimeSeries_DateLocator, TimeSeries_TimedeltaFormatter
  import pandas.tseries.frequencies
  from pandas.tseries.offsets import DateOffset
label_desc: Use image node_id 12 for calling a global function with example usage: _maybe_convert_index(ax, data) and returns: data