code: def read_str(s, start_position):
      """
      If a Python string literal begins at the specified position in the
      given string, then return a tuple ``(val, end_position)``
      containing the value of the string literal and the position where
      it ends.  Otherwise, raise a ``ReadError``.
  
      :param s: A string that will be checked to see if within which a
          Python string literal exists.
      :type s: str
  
      :param start_position: The specified beginning position of the string ``s``
          to begin regex matching.
      :type start_position: int
  
      :return: A tuple containing the matched string literal evaluated as a
          string and the end position of the string literal.
      :rtype: tuple(str, int)
  
      :raise ReadError: If the ``_STRING_START_RE`` regex doesn't return a
          match in ``s`` at ``start_position``, i.e., open quote. If the
          ``_STRING_END_RE`` regex doesn't return a match in ``s`` at the
          end of the first match, i.e., close quote.
      :raise ValueError: If an invalid string (i.e., contains an invalid
          escape sequence) is passed into the ``eval``.
  
      :Example:
  
      >>> from nltk.internals import read_str
      >>> read_str('"Hello", World!', 0)
      ('Hello', 7)
  
      """
      # Read the open quote, and any modifiers.
      m = _STRING_START_RE.match(s, start_position)
      if not m:
          raise ReadError("open quote", start_position)
      quotemark = m.group(1)
  
      # Find the close quote.
      _STRING_END_RE = re.compile(r"\\|%s" % quotemark)
      position = m.end()
      while True:
          match = _STRING_END_RE.search(s, position)
          if not match:
              raise ReadError("close quote", position)
          if match.group(0) == "\\":
              position = match.end() + 1
          else:
              break
  
      # Process it, using eval.  Strings with invalid escape sequences
      # might raise ValueError.
      try:
          return eval(s[start_position : match.end()]), match.end()
      except ValueError as e:
          raise ReadError(
              "valid escape sequence", start_position
          ) from e
  
imports: import fnmatch
  import locale
  import os
  import re
  import stat
  import subprocess
  import sys
  import textwrap
  import types
  import warnings
  from xml.etree import ElementTree
label_desc: Use image node_id 3 for calling a global function with example usage: read_str(s, start_position) and returns: eval,  match