cpython/Lib/exceptions.py

"""Class based built-in exception hierarchy.

New with Python 1.5, all standard built-in exceptions are now class objects by
default.  This gives Python's exception handling mechanism a more
object-oriented feel.  Traditionally they were string objects.  Python will
fallback to string based exceptions if the interpreter is invoked with the -X
option, or if some failure occurs during class exception initialization (in
this case a warning will be printed).

Most existing code should continue to work with class based exceptions.  Some
tricky uses of IOError may break, but the most common uses should work.

Here is a rundown of the class hierarchy.  You can change this by editing this
file, but it isn't recommended.  The class names described here are expected
to be found by the bltinmodule.c file.  If you add classes here, you must
modify bltinmodule.c or the exceptions won't be available in the __builtin__
module, nor will they be accessible from C.

The classes with a `*' are new since Python 1.5.  They are defined as tuples
containing the derived exceptions when string-based exceptions are used.  If
you define your own class based exceptions, they should be derived from
Exception.

Exception(*)
 |
 +-- StandardError(*)
      |
      +-- SystemExit
      +-- KeyboardInterrupt
      +-- ImportError
      +-- EnvironmentError(*)
      |    |
      |    +-- IOError
      |    +-- OSError(*)
      |
      +-- EOFError
      +-- RuntimeError
      |    |
      |    +-- NotImplementedError(*)
      |
      +-- NameError
      +-- AttributeError
      +-- SyntaxError
      +-- TypeError
      +-- AssertionError
      +-- LookupError(*)
      |    |
      |    +-- IndexError
      |    +-- KeyError
      |
      +-- ArithmeticError(*)
      |    |
      |    +-- OverflowError
      |    +-- ZeroDivisionError
      |    +-- FloatingPointError
      |
      +-- ValueError
      +-- SystemError
      +-- MemoryError
"""

class Exception:
    def __init__(self, *args):
        self.args = args

    def __str__(self):
        if not self.args:
            return ''
        elif len(self.args) == 1:
            return str(self.args[0])
        else:
            return str(self.args)

    def __getitem__(self, i):
        return self.args[i]

class StandardError(Exception):
    pass

class SyntaxError(StandardError):
    filename = lineno = offset = text = None
    msg = ""
    def __init__(self, *args):
        self.args = args
        if len(self.args) >= 1:
            self.msg = self.args[0]
        if len(self.args) == 2:
            info = self.args[1]
            try:
                self.filename, self.lineno, self.offset, self.text = info
            except:
                pass
    def __str__(self):
        return str(self.msg)

class EnvironmentError(StandardError):
    """Base class for exceptions that occur outside the Python system.
    Primarily used as a base class for OSError and IOError."""
    def __init__(self, *args):
        self.args = args
        self.errno = None
        self.strerror = None
        self.filename = None
        if len(args) == 3:
            # open() errors give third argument which is the filename.  BUT,
            # so common in-place unpacking doesn't break, e.g.:
            #
            # except IOError, (errno, strerror):
            #
            # we hack args so that it only contains two items.  This also
            # means we need our own __str__() which prints out the filename
            # when it was supplied.
            self.errno, self.strerror, self.filename = args
            self.args = args[0:2]
        if len(args) == 2:
            # common case: PyErr_SetFromErrno()
            self.errno, self.strerror = args

    def __str__(self):
        if self.filename is not None:
            return '[Errno %s] %s: %s' % (self.errno, self.strerror,
                                          repr(self.filename))
        elif self.errno and self.strerror:
            return '[Errno %s] %s' % (self.errno, self.strerror)
        else:
            return StandardError.__str__(self)

class IOError(EnvironmentError):
    pass

class OSError(EnvironmentError):
    """Used by the posix module."""
    pass

class RuntimeError(StandardError):
    pass

class NotImplementedError(RuntimeError):
    pass

class SystemError(StandardError):
    pass

class EOFError(StandardError):
    pass

class ImportError(StandardError):
    pass

class TypeError(StandardError):
    pass

class ValueError(StandardError):
    pass

class KeyboardInterrupt(StandardError):
    pass

class AssertionError(StandardError):
    pass

class ArithmeticError(StandardError):
    pass

class OverflowError(ArithmeticError):
    pass

class FloatingPointError(ArithmeticError):
    pass

class ZeroDivisionError(ArithmeticError):
    pass

class LookupError(StandardError):
    pass

class IndexError(LookupError):
    pass

class KeyError(LookupError):
    pass

class AttributeError(StandardError):
    pass

class NameError(StandardError):
    pass

class MemoryError(StandardError):
    pass

class SystemExit(Exception):
    def __init__(self, *args):
        self.args = args
        if len(args) == 0:
            self.code = None
        elif len(args) == 1:
            self.code = args[0]
        else:
            self.code = args