6. Exceções embutidas

Exceptions should be class objects. The exceptions are defined in the module exceptions. This module never needs to be imported explicitly: the exceptions are provided in the built-in namespace as well as the exceptions module.

For class exceptions, in a try statement with an except clause that mentions a particular class, that clause also handles any exception classes derived from that class (but not exception classes from which it is derived). Two exception classes that are not related via subclassing are never equivalent, even if they have the same name.

The built-in exceptions listed below can be generated by the interpreter or built-in functions. Except where mentioned, they have an “associated value” indicating the detailed cause of the error. This may be a string or a tuple containing several items of information (e.g., an error code and a string explaining the code). The associated value is the second argument to the raise statement. If the exception class is derived from the standard root class BaseException, the associated value is present as the exception instance’s args attribute.

O código do usuário pode gerar exceções embutidas. Isso pode ser usado para testar um manipulador de exceções ou para relatar uma condição de erro “exatamente como” a situação na qual o interpretador gera a mesma exceção; mas lembre-se de que nada impede o código do usuário de gerar um erro inadequado.

As classes de exceção internas podem ser usadas como subclasses para definir novas exceções; Os programadores são incentivados a derivar novas exceções da classe Exception ou de uma de suas subclasses, e não de BaseException. Mais informações sobre a definição de exceções estão disponíveis no Tutorial do Python em Exceções definidas pelo usuário.

The following exceptions are only used as base classes for other exceptions.

exception BaseException

The base class for all built-in exceptions. It is not meant to be directly inherited by user-defined classes (for that, use Exception). If str() or unicode() is called on an instance of this class, the representation of the argument(s) to the instance are returned, or the empty string when there were no arguments.

Novo na versão 2.5.

args

The tuple of arguments given to the exception constructor. Some built-in exceptions (like IOError) expect a certain number of arguments and assign a special meaning to the elements of this tuple, while others are usually called only with a single string giving an error message.

exception Exception

Todas as exceções embutidas que não saem para o sistema são derivadas dessa classe. Todas as exceções definidas pelo usuário também devem ser derivadas dessa classe.

Alterado na versão 2.5: Changed to inherit from BaseException.

exception StandardError

The base class for all built-in exceptions except StopIteration, GeneratorExit, KeyboardInterrupt and SystemExit. StandardError itself is derived from Exception.

exception ArithmeticError

A classe base para as exceções embutidas levantadas para vários erros aritméticos: OverflowError, ZeroDivisionError, FloatingPointError.

exception BufferError

Levantado quando uma operação relacionada a buffer não puder ser realizada.

exception LookupError

A classe base para as exceções levantadas quando uma chave ou índice usado em um mapeamento ou sequência é inválido: IndexError, KeyError. Isso pode ser levantado diretamente por codecs.lookup().

exception EnvironmentError

The base class for exceptions that can occur outside the Python system: IOError, OSError. When exceptions of this type are created with a 2-tuple, the first item is available on the instance’s errno attribute (it is assumed to be an error number), and the second item is available on the strerror attribute (it is usually the associated error message). The tuple itself is also available on the args attribute.

Novo na versão 1.5.2.

When an EnvironmentError exception is instantiated with a 3-tuple, the first two items are available as above, while the third item is available on the filename attribute. However, for backwards compatibility, the args attribute contains only a 2-tuple of the first two constructor arguments.

The filename attribute is None when this exception is created with other than 3 arguments. The errno and strerror attributes are also None when the instance was created with other than 2 or 3 arguments. In this last case, args contains the verbatim constructor arguments as a tuple.

The following exceptions are the exceptions that are actually raised.

exception AssertionError

Levantado quando uma instrução assert falha.

exception AttributeError

Levantado quando uma referência de atributo (consulte attribute-reference) ou atribuição falha. (Quando um objeto não oferece suporte a referências ou atribuições de atributos, TypeError é levantado.)

exception EOFError

Raised when one of the built-in functions (input() or raw_input()) hits an end-of-file condition (EOF) without reading any data. (N.B.: the file.read() and file.readline() methods return an empty string when they hit EOF.)

exception FloatingPointError

Raised when a floating point operation fails. This exception is always defined, but can only be raised when Python is configured with the --with-fpectl option, or the WANT_SIGFPE_HANDLER symbol is defined in the pyconfig.h file.

exception GeneratorExit

Raised when a generator’s close() method is called. It directly inherits from BaseException instead of StandardError since it is technically not an error.

Novo na versão 2.5.

Alterado na versão 2.6: Changed to inherit from BaseException.

exception IOError

Raised when an I/O operation (such as a print statement, the built-in open() function or a method of a file object) fails for an I/O-related reason, e.g., “file not found” or “disk full”.

This class is derived from EnvironmentError. See the discussion above for more information on exception instance attributes.

Alterado na versão 2.6: Changed socket.error to use this as a base class.

exception ImportError

Raised when an import statement fails to find the module definition or when a from ... import fails to find a name that is to be imported.

exception IndexError

Raised when a sequence subscript is out of range. (Slice indices are silently truncated to fall in the allowed range; if an index is not a plain integer, TypeError is raised.)

exception KeyError

Raised when a mapping (dictionary) key is not found in the set of existing keys.

exception KeyboardInterrupt

Raised when the user hits the interrupt key (normally Control-C or Delete). During execution, a check for interrupts is made regularly. Interrupts typed when a built-in function input() or raw_input() is waiting for input also raise this exception. The exception inherits from BaseException so as to not be accidentally caught by code that catches Exception and thus prevent the interpreter from exiting.

Alterado na versão 2.5: Changed to inherit from BaseException.

exception MemoryError

Raised when an operation runs out of memory but the situation may still be rescued (by deleting some objects). The associated value is a string indicating what kind of (internal) operation ran out of memory. Note that because of the underlying memory management architecture (C’s malloc() function), the interpreter may not always be able to completely recover from this situation; it nevertheless raises an exception so that a stack traceback can be printed, in case a run-away program was the cause.

exception NameError

Levantada quando um nome local ou global não é encontrado. Isso se aplica apenas a nomes não qualificados. O valor associado é uma mensagem de erro que inclui o nome que não pode ser encontrado.

exception NotImplementedError

This exception is derived from RuntimeError. In user defined base classes, abstract methods should raise this exception when they require derived classes to override the method.

Novo na versão 1.5.2.

exception OSError

This exception is derived from EnvironmentError. It is raised when a function returns a system-related error (not for illegal argument types or other incidental errors). The errno attribute is a numeric error code from errno, and the strerror attribute is the corresponding string, as would be printed by the C function perror(). See the module errno, which contains names for the error codes defined by the underlying operating system.

For exceptions that involve a file system path (such as chdir() or unlink()), the exception instance will contain a third attribute, filename, which is the file name passed to the function.

Novo na versão 1.5.2.

exception OverflowError

Raised when the result of an arithmetic operation is too large to be represented. This cannot occur for long integers (which would rather raise MemoryError than give up) and for most operations with plain integers, which return a long integer instead. Because of the lack of standardization of floating point exception handling in C, most floating point operations also aren’t checked.

exception ReferenceError

This exception is raised when a weak reference proxy, created by the weakref.proxy() function, is used to access an attribute of the referent after it has been garbage collected. For more information on weak references, see the weakref module.

Novo na versão 2.2: Previously known as the weakref.ReferenceError exception.

exception RuntimeError

Levantada quando um erro é detectado e não se encaixa em nenhuma das outras categorias. O valor associado é uma string indicando o que precisamente deu errado.

exception StopIteration

Raised by an iterator’s next() method to signal that there are no further values. This is derived from Exception rather than StandardError, since this is not considered an error in its normal application.

Novo na versão 2.2.

exception SyntaxError

Raised when the parser encounters a syntax error. This may occur in an import statement, in an exec statement, in a call to the built-in function eval() or input(), or when reading the initial script or standard input (also interactively).

Instances of this class have attributes filename, lineno, offset and text for easier access to the details. str() of the exception instance returns only the message.

exception IndentationError

Classe base para erros de sintaxe relacionados a indentação incorreta. Esta é uma subclasse de SyntaxError.

exception TabError

Raised when indentation contains an inconsistent use of tabs and spaces. This is a subclass of IndentationError.

exception SystemError

Raised when the interpreter finds an internal error, but the situation does not look so serious to cause it to abandon all hope. The associated value is a string indicating what went wrong (in low-level terms).

You should report this to the author or maintainer of your Python interpreter. Be sure to report the version of the Python interpreter (sys.version; it is also printed at the start of an interactive Python session), the exact error message (the exception’s associated value) and if possible the source of the program that triggered the error.

exception SystemExit

This exception is raised by the sys.exit() function. When it is not handled, the Python interpreter exits; no stack traceback is printed. If the associated value is a plain integer, it specifies the system exit status (passed to C’s exit() function); if it is None, the exit status is zero; if it has another type (such as a string), the object’s value is printed and the exit status is one.

Instances have an attribute code which is set to the proposed exit status or error message (defaulting to None). Also, this exception derives directly from BaseException and not StandardError, since it is not technically an error.

A call to sys.exit() is translated into an exception so that clean-up handlers (finally clauses of try statements) can be executed, and so that a debugger can execute a script without running the risk of losing control. The os._exit() function can be used if it is absolutely positively necessary to exit immediately (for example, in the child process after a call to os.fork()).

The exception inherits from BaseException instead of StandardError or Exception so that it is not accidentally caught by code that catches Exception. This allows the exception to properly propagate up and cause the interpreter to exit.

Alterado na versão 2.5: Changed to inherit from BaseException.

exception TypeError

Raised when an operation or function is applied to an object of inappropriate type. The associated value is a string giving details about the type mismatch.

exception UnboundLocalError

Raised when a reference is made to a local variable in a function or method, but no value has been bound to that variable. This is a subclass of NameError.

Novo na versão 2.0.

exception UnicodeError

Raised when a Unicode-related encoding or decoding error occurs. It is a subclass of ValueError.

UnicodeError has attributes that describe the encoding or decoding error. For example, err.object[err.start:err.end] gives the particular invalid input that the codec failed on.

encoding

The name of the encoding that raised the error.

reason

A string describing the specific codec error.

object

The object the codec was attempting to encode or decode.

start

The first index of invalid data in object.

end

The index after the last invalid data in object.

Novo na versão 2.0.

exception UnicodeEncodeError

Raised when a Unicode-related error occurs during encoding. It is a subclass of UnicodeError.

Novo na versão 2.3.

exception UnicodeDecodeError

Raised when a Unicode-related error occurs during decoding. It is a subclass of UnicodeError.

Novo na versão 2.3.

exception UnicodeTranslateError

Raised when a Unicode-related error occurs during translating. It is a subclass of UnicodeError.

Novo na versão 2.3.

exception ValueError

Raised when an operation or function receives an argument that has the right type but an inappropriate value, and the situation is not described by a more precise exception such as IndexError.

exception VMSError

Only available on VMS. Raised when a VMS-specific error occurs.

exception WindowsError

Raised when a Windows-specific error occurs or when the error number does not correspond to an errno value. The winerror and strerror values are created from the return values of the GetLastError() and FormatMessage() functions from the Windows Platform API. The errno value maps the winerror value to corresponding errno.h values. This is a subclass of OSError.

Novo na versão 2.0.

Alterado na versão 2.5: Previous versions put the GetLastError() codes into errno.

exception ZeroDivisionError

Raised when the second argument of a division or modulo operation is zero. The associated value is a string indicating the type of the operands and the operation.

The following exceptions are used as warning categories; see the warnings module for more information.

exception Warning

Base class for warning categories.

exception UserWarning

Base class for warnings generated by user code.

exception DeprecationWarning

Base class for warnings about deprecated features.

exception PendingDeprecationWarning

Base class for warnings about features which will be deprecated in the future.

exception SyntaxWarning

Base class for warnings about dubious syntax.

exception RuntimeWarning

Base class for warnings about dubious runtime behavior.

exception FutureWarning

Base class for warnings about constructs that will change semantically in the future.

exception ImportWarning

Base class for warnings about probable mistakes in module imports.

Novo na versão 2.5.

exception UnicodeWarning

Base class for warnings related to Unicode.

Novo na versão 2.5.

exception BytesWarning

Base class for warnings related to bytes and bytearray.

Novo na versão 2.6.

6.1. Exception hierarchy

The class hierarchy for built-in exceptions is:

BaseException
 +-- SystemExit
 +-- KeyboardInterrupt
 +-- GeneratorExit
 +-- Exception
      +-- StopIteration
      +-- StandardError
      |    +-- BufferError
      |    +-- ArithmeticError
      |    |    +-- FloatingPointError
      |    |    +-- OverflowError
      |    |    +-- ZeroDivisionError
      |    +-- AssertionError
      |    +-- AttributeError
      |    +-- EnvironmentError
      |    |    +-- IOError
      |    |    +-- OSError
      |    |         +-- WindowsError (Windows)
      |    |         +-- VMSError (VMS)
      |    +-- EOFError
      |    +-- ImportError
      |    +-- LookupError
      |    |    +-- IndexError
      |    |    +-- KeyError
      |    +-- MemoryError
      |    +-- NameError
      |    |    +-- UnboundLocalError
      |    +-- ReferenceError
      |    +-- RuntimeError
      |    |    +-- NotImplementedError
      |    +-- SyntaxError
      |    |    +-- IndentationError
      |    |         +-- TabError
      |    +-- SystemError
      |    +-- TypeError
      |    +-- ValueError
      |         +-- UnicodeError
      |              +-- UnicodeDecodeError
      |              +-- UnicodeEncodeError
      |              +-- UnicodeTranslateError
      +-- Warning
           +-- DeprecationWarning
           +-- PendingDeprecationWarning
           +-- RuntimeWarning
           +-- SyntaxWarning
           +-- UserWarning
           +-- FutureWarning
	   +-- ImportWarning
	   +-- UnicodeWarning
	   +-- BytesWarning