python - Python: 分離されたモジュールの例外が正しく動作しない

Question

新しい例外クラスを作成し、OSError クラスのようにエラーを表現したいと思います。ここに私が欲しいものがあります:

>>> raise(MyError(1, 'info'))
MyError: [Errno 1] predefined text: info

私は何をすべきか？基本例外クラスから継承した場合、これを行うことはできますか? これが私が試したことです（gnulibで動作するモジュールの例）：

class GNULibError(Exception):
  '''Exception handler for GNULib classes.'''

  def __init__(self, errno, errinfo=None):
    '''Each error has following parameters:
    errno: code of error; used to catch error type
      1: destination directory does not exist: <destdir>
      2: configure file does not exist: <configure.ac>
      3: selected module does not exist: <module>
      4: <cache> is expected to contain gl_M4_BASE([m4base])
      5: missing sourcebase argument
      6: missing docbase argument
      7: missing testsbase argument
      8: missing libname argument
    errinfo: additional info'''
    self.errno = errno; self.errinfo = errinfo
    self.args = (self.errno, self.errinfo)

  def __str__(self):
    errors = \
    [ # Begin list of errors
      "destination directory does not exist: %s" % self.errinfo,
      "configure file does not exist: %s" % self.errinfo,
      "selected module does not exist: %s" % self.errinfo,
      "%s is expected to contain gl_M4_BASE([%s])" % \
        (os.path.join(self.errinfo, 'gnulib-comp.m4'), self.errinfo),
      "missing sourcebase argument; cache file doesn't contain it,"
        +" so you might have to set this argument",
      "missing docbase argument; you might have to create GNULibImport" \
        +" instance with mode 0 and docbase argument",
      "missing testsbase argument; cache file doesn't contain it,"
        +" so you might have to set this argument"
      "missing libname argument; cache file doesn't contain it,"
        +" so you might have to set this argument",
      "dependencies and testflag 'default' cannot be used together",
    ] # Complete list of errors
    if not PYTHON3:
      self.message = (b'[Errno %d] %s' % \
        (self.errno, errors[self.errno -1].encode(ENCS['default'])))
    else: # if PYTHON3
      self.message = ('[Errno %d] %s' % \
        (self.errno, errors[self.errno -1]))
    return(self.message)

それは間違って動作し、Python 2 ではエラー名のみを返し、Python 3 では空の文字列を返します。ありがとう！

Answer 1

__str__ の代わりに __repr__ メソッドを実装する必要があります

http://docs.python.org/reference/datamodel.html#object.__repr__

それはうまくいきます：

 class GNULibError(Exception):
  '''Exception handler for GNULib classes.'''

  def __init__(self, errno, errinfo=None):
    '''Each error has following parameters:
    errno: code of error; used to catch error type
      1: destination directory does not exist: <destdir>
      2: configure file does not exist: <configure.ac>
      3: selected module does not exist: <module>
      4: <cache> is expected to contain gl_M4_BASE([m4base])
      5: missing sourcebase argument
      6: missing docbase argument
      7: missing testsbase argument
      8: missing libname argument
    errinfo: additional info'''
    self.errno = errno; self.errinfo = errinfo
    self.args = (self.errno, self.errinfo)

  def __repr__(self):
    errors = \
    [ # Begin list of errors
      "destination directory does not exist: %s" % self.errinfo,
      "configure file does not exist: %s" % self.errinfo,
      "selected module does not exist: %s" % self.errinfo,
      "%s is expected to contain gl_M4_BASE([%s])" % \
        (os.path.join(self.errinfo, 'gnulib-comp.m4'), self.errinfo),
      "missing sourcebase argument; cache file doesn't contain it,"
        +" so you might have to set this argument",
      "missing docbase argument; you might have to create GNULibImport" \
        +" instance with mode 0 and docbase argument",
      "missing testsbase argument; cache file doesn't contain it,"
        +" so you might have to set this argument"
      "missing libname argument; cache file doesn't contain it,"
        +" so you might have to set this argument",
      "dependencies and testflag 'default' cannot be used together",
    ] # Complete list of errors
    if not PYTHON3:
      self.message = (b'[Errno %d] %s' % \
        (self.errno, errors[self.errno -1].encode(ENCS['default'])))
    else: # if PYTHON3
      self.message = ('[Errno %d] %s' % \
        (self.errno, errors[self.errno -1]))
    return(self.message)