code: def maybe_upcast(values, fill_value=np.nan, dtype=None, copy=False):
      """provide explicit type promotion and coercion
  
      Parameters
      ----------
      values : the ndarray that we want to maybe upcast
      fill_value : what we want to fill with
      dtype : if None, then use the dtype of the values, else coerce to this type
      copy : if True always make a copy even if no upcast is required
      """
  
      if is_extension_type(values):
          if copy:
              values = values.copy()
      else:
          if dtype is None:
              dtype = values.dtype
          new_dtype, fill_value = maybe_promote(dtype, fill_value)
          if new_dtype != values.dtype:
              values = values.astype(new_dtype)
          elif copy:
              values = values.copy()
  
      return values, fill_value
  
imports: from datetime import datetime, timedelta
  import numpy
  from pandas._libs import lib, tslib, tslibs
  from pandas._libs.tslibs import NaT, OutOfBoundsDatetime, Period, iNaT
  from pandas.compat import PY3, string_types, text_type, to_str
  from .common import _INT64_DTYPE, _NS_DTYPE, _POSSIBLY_CAST_DTYPES, _TD_DTYPE, ensure_int8, ensure_int16, ensure_int32, ensure_int64, ensure_object, is_bool, is_bool_dtype, is_categorical_dtype, is_complex, is_complex_dtype, is_datetime64_dtype, is_datetime64_ns_dtype, is_datetime64tz_dtype, is_datetime_or_timedelta_dtype, is_datetimelike, is_dtype_equal, is_extension_array_dtype, is_extension_type, is_float, is_float_dtype, is_integer, is_integer_dtype, is_object_dtype, is_scalar, is_string_dtype, is_timedelta64_dtype, is_timedelta64_ns_dtype, is_unsigned_integer_dtype, pandas_dtype
  from .dtypes import DatetimeTZDtype, ExtensionDtype, PandasExtensionDtype, PeriodDtype
  from .generic import ABCDatetimeArray, ABCDatetimeIndex, ABCPeriodArray, ABCPeriodIndex, ABCSeries
  from .inference import is_list_like
  from .missing import isna, notna
label_desc: Use image node_id 10 for calling a global function with example usage: maybe_upcast(values, fill_value, dtype, copy) and returns: values,  fill_value