class_docstr: Factory class for function transforming a string into another object
  (int, float).
  
  After initialization, an instance can be called to transform a string
  into another object. If the string is recognized as representing a
  missing value, a default value is returned.
  
  Attributes
  ----------
  func : function
      Function used for the conversion.
  default : any
      Default value to return when the input corresponds to a missing
      value.
  type : type
      Type of the output.
  _status : int
      Integer representing the order of the conversion.
  _mapper : sequence of tuples
      Sequence of tuples (dtype, function, default value) to evaluate in
      order.
  _locked : bool
      Holds `locked` parameter.
  
  Parameters
  ----------
  dtype_or_func : {None, dtype, function}, optional
      If a `dtype`, specifies the input data type, used to define a basic
      function and a default value for missing data. For example, when
      `dtype` is float, the `func` attribute is set to `float` and the
      default value to `np.nan`.  If a function, this function is used to
      convert a string to another object. In this case, it is recommended
      to give an associated default value as input.
  default : any, optional
      Value to return by default, that is, when the string to be
      converted is flagged as missing. If not given, `StringConverter`
      tries to supply a reasonable default value.
  missing_values : {None, sequence of str}, optional
      ``None`` or sequence of strings indicating a missing value. If ``None``
      then missing values are indicated by empty entries. The default is
      ``None``.
  locked : bool, optional
      Whether the StringConverter should be locked to prevent automatic
      upgrade or not. Default is False.
code: def __call__(self, value):
      return self._callingfunction(value)
  
imports: import numpy
  import numpy._core.numeric
  from numpy._utils import asbytes, asunicode
label_desc: Use image node_id 9 for calling the StringConverter obj's underlying member method code with example usage: obj.__call__(value) and returns: self