code: def _convert_expression(expr) -> str:
      """
      Convert an object to an expression.
  
      This function converts an object to an expression (a unicode string) and
      checks to make sure it isn't empty after conversion. This is used to
      convert operators to their string representation for recursive calls to
      :func:`~pandas.eval`.
  
      Parameters
      ----------
      expr : object
          The object to be converted to a string.
  
      Returns
      -------
      str
          The string representation of an object.
  
      Raises
      ------
      ValueError
        * If the expression is empty.
      """
      s = pprint_thing(expr)
      _check_expression(s)
      return s
  
file_path: catboost/contrib/python/pandas/py3/pandas/core/computation/eval.py
imports: from __future__ import annotations
  import tokenize
  from typing import TYPE_CHECKING
  import warnings
  from pandas.util._exceptions import find_stack_level
  from pandas.util._validators import validate_bool_kwarg
  from pandas.core.dtypes.common import is_extension_array_dtype
  from pandas.core.computation.engines import ENGINES
  from pandas.core.computation.expr import PARSERS, Expr
  from pandas.core.computation.parsing import tokenize_string
  from pandas.core.computation.scope import ensure_scope
  from pandas.core.generic import NDFrame
  from pandas.io.formats.printing import pprint_thing
label_desc: Use image node_id 5 for calling a global function with example usage: _convert_expression(expr) and returns: s