# `traceback` — Print or retrieve a stack traceback

Código fuente: Lib/traceback.py

This module provides a standard interface to extract, format and print stack traces of Python programs. It is more flexible than the interpreter’s default traceback display, and therefore makes it possible to configure certain aspects of the output. Finally, it contains a utility for capturing enough information about an exception to print it later, without the need to save a reference to the actual exception. Since exceptions can be the roots of large objects graph, this utility can significantly improve memory management.

The module uses traceback objects — these are objects of type `types.TracebackType`, which are assigned to the `__traceback__` field of `BaseException` instances.

Ver también

Módulo `faulthandler`

  Usado para volcar explícitamente los rastreos Python, en un error, después de un tiempo de espera (timeout), o en una señal de usuario.

Módulo `pdb`

  Depurador interactivo de código fuente para programas Python.

The module’s API can be divided into two parts:

- Module-level functions offering basic functionality, which are useful for interactive inspection of exceptions and tracebacks.

- `TracebackException` class and its helper classes `StackSummary` and `FrameSummary`. These offer both more flexibility in the output generated and the ability to store the information necessary for later formatting without holding references to actual exception and traceback objects.

## Module-Level Functions

traceback.print_tb(tb, limit=None, file=None)

  Print up to limit stack trace entries from traceback object tb (starting from the caller’s frame) if limit is positive. Otherwise, print the last `abs(limit)` entries. If limit is omitted or `None`, all entries are printed. If file is omitted or `None`, the output goes to `sys.stderr`; otherwise it should be an open file or file-like object to receive the output.

  Nota

  The meaning of the limit parameter is different than the meaning of `sys.tracebacklimit`. A negative limit value corresponds to a positive value of `sys.tracebacklimit`, whereas the behaviour of a positive limit value cannot be achieved with `sys.tracebacklimit`.

  Distinto en la versión 3.5: Soporte para limit negativo añadido.

traceback.print_exception(exc, /, [value, tb, ]limit=None, file=None, chain=True)

  Print exception information and stack trace entries from traceback object tb to file. This differs from `print_tb()` in the following ways:

  - si tb no es `None`, muestra una cabecera `Traceback (most recent call last):`

  - imprime el tipo de excepción y value después del seguimiento de la pila

  - si type(value) es `SyntaxError` y value tiene el formato apropiado, muestra la línea donde el error sintáctico ha ocurrido con un cursor indicando la posición aproximada del error.

  Desde Python 3.10, en lugar de pasar value y tb, se puede pasar un objeto de excepción como primer argumento. Si se proporcionan value y tb, el primer argumento se ignora para proporcionar compatibilidad con versiones anteriores.

  The optional limit argument has the same meaning as for `print_tb()`. If chain is true (the default), then chained exceptions (the `__cause__` or `__context__` attributes of the exception) will be printed as well, like the interpreter itself does when printing an unhandled exception.

  Distinto en la versión 3.5: El argumento etype es ignorado e infiere desde el tipo de value.

  Distinto en la versión 3.10: El parámetro etype ha cambiado de nombre a exc y ahora es solo posicional.

traceback.print_exc(limit=None, file=None, chain=True)

  This is a shorthand for `print_exception(sys.exception(), limit=limit, file=file, chain=chain)`.

traceback.print_last(limit=None, file=None, chain=True)

  This is a shorthand for `print_exception(sys.last_exc, limit=limit, file=file, chain=chain)`. In general it will work only after an exception has reached an interactive prompt (see `sys.last_exc`).

traceback.print_stack(f=None, limit=None, file=None)

  Print up to limit stack trace entries (starting from the invocation point) if limit is positive. Otherwise, print the last `abs(limit)` entries. If limit is omitted or `None`, all entries are printed. The optional f argument can be used to specify an alternate stack frame to start. The optional file argument has the same meaning as for `print_tb()`.

  Distinto en la versión 3.5: Soporte para limit negativo añadido.

traceback.extract_tb(tb, limit=None)

  Return a `StackSummary` object representing a list of «pre-processed» stack trace entries extracted from the traceback object tb. It is useful for alternate formatting of stack traces. The optional limit argument has the same meaning as for `print_tb()`. A «pre-processed» stack trace entry is a `FrameSummary` object containing attributes `filename`, `lineno`, `name`, and `line` representing the information that is usually printed for a stack trace.

traceback.extract_stack(f=None, limit=None)

  Extract the raw traceback from the current stack frame. The return value has the same format as for `extract_tb()`. The optional f and limit arguments have the same meaning as for `print_stack()`.

traceback.print_list(extracted_list, file=None)

  Print the list of tuples as returned by `extract_tb()` or `extract_stack()` as a formatted stack trace to the given file. If file is `None`, the output is written to `sys.stderr`.

traceback.format_list(extracted_list)

  Dada una lista de tuplas u objetos `FrameSummary` según lo retornado por `extract_tb()` o `extract_stack()`, retorna una lista de cadenas preparadas para ser mostradas. Cada cadena en la lista resultante corresponde con el elemento con el mismo índice en la lista de argumentos. Cada cadena finaliza en una nueva línea; las cadenas pueden contener nuevas líneas internas también, para aquellos elementos cuya línea de texto de origen no es `None`.

traceback.format_exception_only(exc, /[, value])

  Format the exception part of a traceback using an exception value such as given by `sys.last_value`. The return value is a list of strings, each ending in a newline. The list contains the exception’s message, which is normally a single string; however, for `SyntaxError` exceptions, it contains several lines that (when printed) display detailed information about where the syntax error occurred. Following the message, the list contains the exception’s `notes`.

  Desde Python 3,10, en lugar de pasar value, un objeto de excepción se puede pasar como primer argumento. Si se proporciona value, el primer argumento se ignora el fin de proporcionar compatibilidad hacia atrás.

  Distinto en la versión 3.10: El parámetro etype ha cambiado de nombre a exc y ahora es solo posicional.

  Distinto en la versión 3.11: The returned list now includes any `notes` attached to the exception.

traceback.format_exception(exc, /, [value, tb, ]limit=None, chain=True)

  Formatea una traza de pila y la información de la excepción. Los argumentos tienen el mismo significado que los argumentos correspondientes a `print_exception()`. El valor retornado es una lista de cadenas, acabando cada una en una nueva línea y algunas contienen nuevas líneas internas. Cuando estas líneas son concatenadas y mostradas, exactamente el mismo texto es mostrado como hace `print_exception()`.

  Distinto en la versión 3.5: El argumento etype es ignorado e infiere desde el tipo de value.

  Distinto en la versión 3.10: El comportamiento y la firma de esta función se modificaron para coincidir con `print_exception()`.

traceback.format_exc(limit=None, chain=True)

  Esto es como `print_exc(limit)` pero retorna una cadena en lugar de imprimirlo en un archivo.

traceback.format_tb(tb, limit=None)

  Un atajo para `format_list(extract_tb(tb, limit))`.

traceback.format_stack(f=None, limit=None)

  Un atajo para `format_list(extract_stack(f, limit))`.

traceback.clear_frames(tb)

  Clears the local variables of all the stack frames in a traceback tb by calling the `clear()` method of each frame object.

  Added in version 3.4.

traceback.walk_stack(f)

  Walk a stack following `f.f_back` from the given frame, yielding the frame and line number for each frame. If f is `None`, the current stack is used. This helper is used with `StackSummary.extract()`.

  Added in version 3.5.

traceback.walk_tb(tb)

  Walk a traceback following `tb_next` yielding the frame and line number for each frame. This helper is used with `StackSummary.extract()`.

  Added in version 3.5.

## `TracebackException` Objects

Added in version 3.5.

`TracebackException` objects are created from actual exceptions to capture data for later printing. They offer a more lightweight method of storing this information by avoiding holding references to traceback and frame objects. In addition, they expose more options to configure the output compared to the module-level functions described above.

class traceback.TracebackException(exc_type, exc_value, exc_traceback, *, limit=None, lookup_lines=True, capture_locals=False, compact=False, max_group_width=15, max_group_depth=10)

  Capture an exception for later rendering. The meaning of limit, lookup_lines and capture_locals are as for the `StackSummary` class.

  If compact is true, only data that is required by `TracebackException`’s `format()` method is saved in the class attributes. In particular, the `__context__` field is calculated only if `__cause__` is `None` and `__suppress_context__` is false.

  Tenga en cuenta que cuando se capturan locales, también se muestran en el rastreo.

  max_group_width (anchura máxima del grupo) y max_group_depth (profundidad máxima del grupo) controlan el formato del grupo de excepciones (ver `BaseExceptionGroup`). La profundidad (depth) se refiere al nivel de anidamiento del grupo, y la anchura (width) se refiere al tamaño de una excepción simple perteneciente al arreglo del grupo de excepciones. El formato de salida se trunca cuando se excede el límite.

  Distinto en la versión 3.10: Se agregó el parámetro compact.

  Distinto en la versión 3.11: Se agregaron los parámetros max_group_width y max_group_depth

  __cause__

    A `TracebackException` of the original `__cause__`.

  __context__

    A `TracebackException` of the original `__context__`.

  exceptions

    If `self` represents an `ExceptionGroup`, this field holds a list of `TracebackException` instances representing the nested exceptions. Otherwise it is `None`.

    Added in version 3.11.

  __suppress_context__

    The `__suppress_context__` value from the original exception.

  __notes__

    The `__notes__` value from the original exception, or `None` if the exception does not have any notes. If it is not `None` is it formatted in the traceback after the exception string.

    Added in version 3.11.

  stack

    Una clase `StackSummary` representando el seguimiento de pila.

  exc_type

    La clase del seguimiento de pila original.

  filename

    Para errores sintácticos - el nombre del archivo donde el error ha ocurrido.

  lineno

    Para errores sintácticos - el número de línea donde el error ha ocurrido.

  end_lineno

    Para errores sintácticos - el número de línea donde el error ha ocurrido. Puede ser `None` si no está presente.

    Added in version 3.10.

  text

    Para errores sintácticos - el texto donde el error ha ocurrido.

  offset

    Para errores sintácticos - el offset en el texto donde el error ha ocurrido.

  end_offset

    Para errores sintácticos - el offset en el texto donde el error ha ocurrido. Puede ser `None` si no está presente.

    Added in version 3.10.

  msg

    Para errores sintácticos - el mensaje de error del compilador.

  classmethod from_exception(exc, *, limit=None, lookup_lines=True, capture_locals=False)

    Captura una excepción para su posterior procesado. limit, lookup_lines y capture_locals son como para la clase `StackSummary`.

    Tenga en cuenta que cuando se capturan locales, también se muestran en el rastreo.

  print(*, file=None, chain=True)

    Imprime en file (`sys.stderr` por defecto) la información de la excepción retornada por `format()`.

    Added in version 3.11.

  format(*, chain=True)

    Formatea la excepción.

    If chain is not `True`, `__cause__` and `__context__` will not be formatted.

    El valor retornado es un generador de cadenas, donde cada una acaba en una nueva línea y algunas contienen nuevas líneas internas. `print_exception()` es un contenedor alrededor de este método que simplemente muestra las líneas de un archivo.

  format_exception_only()

    Formatea la parte de la excepción de un seguimiento de pila.

    El valor retornado es un generador de cadenas, donde cada una acaba en una nueva línea.

    El generador emite el mensaje de la excepción seguida por sus notas (si tiene alguna). El mensaje de excepción es normalmente una sola cadena; , sin embargo, para excepciones `SyntaxError`, este emite múltiples líneas que (cuando son mostradas) imprimen información detallada sobre dónde ha ocurrido el error sintáctico.

    Distinto en la versión 3.11: The exception’s `notes` are now included in the output.

## `StackSummary` Objects

Added in version 3.5.

`StackSummary` objects represent a call stack ready for formatting.

class traceback.StackSummary
  classmethod extract(frame_gen, *, limit=None, lookup_lines=True, capture_locals=False)

    Construct a `StackSummary` object from a frame generator (such as is returned by `walk_stack()` or `walk_tb()`).

    If limit is supplied, only this many frames are taken from frame_gen. If lookup_lines is `False`, the returned `FrameSummary` objects will not have read their lines in yet, making the cost of creating the `StackSummary` cheaper (which may be valuable if it may not actually get formatted). If capture_locals is `True` the local variables in each `FrameSummary` are captured as object representations.

    Distinto en la versión 3.12: Las excepciones lanzadas desde `repr()` en una variable local (cuando capture_locals es `True`) no son propagadas al invocador.

  classmethod from_list(a_list)

    Construct a `StackSummary` object from a supplied list of `FrameSummary` objects or old-style list of tuples. Each tuple should be a 4-tuple with filename, lineno, name, line as the elements.

  format()

    Returns a list of strings ready for printing. Each string in the resulting list corresponds to a single frame from the stack. Each string ends in a newline; the strings may contain internal newlines as well, for those items with source text lines.

    Para secuencias largas del mismo marco y línea, se muestran las primeras repeticiones, seguidas de una línea de resumen que indica el número exacto de repeticiones adicionales.

    Distinto en la versión 3.6: Las secuencias largas de cuadros repetidos ahora se abrevian.

  format_frame_summary(frame_summary)

    Returns a string for printing one of the frames involved in the stack. This method is called for each `FrameSummary` object to be printed by `StackSummary.format()`. If it returns `None`, the frame is omitted from the output.

    Added in version 3.11.

## `FrameSummary` Objects

Added in version 3.5.

A `FrameSummary` object represents a single frame in a traceback.

class traceback.FrameSummary(filename, lineno, name, *, lookup_line=True, locals=None, line=None, end_lineno=None, colno=None, end_colno=None)

  Represents a single frame in the traceback or stack that is being formatted or printed. It may optionally have a stringified version of the frame’s locals included in it. If lookup_line is `False`, the source code is not looked up until the `FrameSummary` has the `line` attribute accessed (which also happens when casting it to a `tuple`). `line` may be directly provided, and will prevent line lookups happening at all. locals is an optional local variable dictionary, and if supplied the variable representations are stored in the summary for later display.

  `FrameSummary` instances have the following attributes:

  filename

    The filename of the source code for this frame. Equivalent to accessing `f.f_code.co_filename` on a frame object f.

  lineno

    The line number of the source code for this frame.

  name

    Equivalent to accessing `f.f_code.co_name` on a frame object f.

  line

    A string representing the source code for this frame, with leading and trailing whitespace stripped. If the source is not available, it is `None`.

  end_lineno

    The last line number of the source code for this frame. By default, it is set to `None` and indexation starts from 1.

  colno

    The column number of the source code for this frame. By default, it is `None` and indexation starts from 0.

  end_colno

    The last column number of the source code for this frame. By default, it is `None` and indexation starts from 0.

## Examples of Using the Module-Level Functions

Este ejemplo sencillo implementa un bucle de lectura, evaluación e impresión básico, similar a (pero menos útil) el bucle del intérprete interactivo estándar de Python. Para una implementación más completa del bucle del intérprete, ir al módulo `code`

    import sys, traceback

    def run_user_code(envdir):
        source = input(">>> ")
        try:
            exec(source, envdir)
        except Exception:
            print("Exception in user code:")
            print("-"*60)
            traceback.print_exc(file=sys.stdout)
            print("-"*60)

    envdir = {}
    while True:
        run_user_code(envdir)

El siguiente ejemplo demuestra las diferentes manera para mostrar y formatear la excepción y el seguimiento de pila:

    import sys, traceback

    def lumberjack():
        bright_side_of_life()

    def bright_side_of_life():
        return tuple()[0]

    try:
        lumberjack()
    except IndexError as exc:
        print("*** print_tb:")
        traceback.print_tb(exc.__traceback__, limit=1, file=sys.stdout)
        print("*** print_exception:")
        traceback.print_exception(exc, limit=2, file=sys.stdout)
        print("*** print_exc:")
        traceback.print_exc(limit=2, file=sys.stdout)
        print("*** format_exc, first and last line:")
        formatted_lines = traceback.format_exc().splitlines()
        print(formatted_lines[0])
        print(formatted_lines[-1])
        print("*** format_exception:")
        print(repr(traceback.format_exception(exc)))
        print("*** extract_tb:")
        print(repr(traceback.extract_tb(exc.__traceback__)))
        print("*** format_tb:")
        print(repr(traceback.format_tb(exc.__traceback__)))
        print("*** tb_lineno:", exc.__traceback__.tb_lineno)

La salida para el ejemplo podría ser similar a esto:

    *** print_tb:
      File "<doctest...>", line 10, in <module>
        lumberjack()
    *** print_exception:
    Traceback (most recent call last):
      File "<doctest...>", line 10, in <module>
        lumberjack()
      File "<doctest...>", line 4, in lumberjack
        bright_side_of_life()
    IndexError: tuple index out of range
    *** print_exc:
    Traceback (most recent call last):
      File "<doctest...>", line 10, in <module>
        lumberjack()
      File "<doctest...>", line 4, in lumberjack
        bright_side_of_life()
    IndexError: tuple index out of range
    *** format_exc, first and last line:
    Traceback (most recent call last):
    IndexError: tuple index out of range
    *** format_exception:
    ['Traceback (most recent call last):\n',
     '  File "<doctest default[0]>", line 10, in <module>\n    lumberjack()\n',
     '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_life()\n',
     '  File "<doctest default[0]>", line 7, in bright_side_of_life\n    return tuple()[0]\n           ~~~~~~~^^^\n',
     'IndexError: tuple index out of range\n']
    *** extract_tb:
    [<FrameSummary file <doctest...>, line 10 in <module>>,
     <FrameSummary file <doctest...>, line 4 in lumberjack>,
     <FrameSummary file <doctest...>, line 7 in bright_side_of_life>]
    *** format_tb:
    ['  File "<doctest default[0]>", line 10, in <module>\n    lumberjack()\n',
     '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_life()\n',
     '  File "<doctest default[0]>", line 7, in bright_side_of_life\n    return tuple()[0]\n           ~~~~~~~^^^\n']
    *** tb_lineno: 10

El siguiente ejemplo muestra las diferentes maneras de imprimir y formatear la pila:

    >>> import traceback
    >>> def another_function():
    ...     lumberstack()
    ...
    >>> def lumberstack():
    ...     traceback.print_stack()
    ...     print(repr(traceback.extract_stack()))
    ...     print(repr(traceback.format_stack()))
    ...
    >>> another_function()
      File "<doctest>", line 10, in <module>
        another_function()
      File "<doctest>", line 3, in another_function
        lumberstack()
      File "<doctest>", line 6, in lumberstack
        traceback.print_stack()
    [('<doctest>', 10, '<module>', 'another_function()'),
     ('<doctest>', 3, 'another_function', 'lumberstack()'),
     ('<doctest>', 7, 'lumberstack', 'print(repr(traceback.extract_stack()))')]
    ['  File "<doctest>", line 10, in <module>\n    another_function()\n',
     '  File "<doctest>", line 3, in another_function\n    lumberstack()\n',
     '  File "<doctest>", line 8, in lumberstack\n    print(repr(traceback.format_stack()))\n']

Este último ejemplo demuestra las últimas funciones de formateo:

    >>> import traceback
    >>> traceback.format_list([('spam.py', 3, '<module>', 'spam.eggs()'),
    ...                        ('eggs.py', 42, 'eggs', 'return "bacon"')])
    ['  File "spam.py", line 3, in <module>\n    spam.eggs()\n',
     '  File "eggs.py", line 42, in eggs\n    return "bacon"\n']
    >>> an_error = IndexError('tuple index out of range')
    >>> traceback.format_exception_only(an_error)
    ['IndexError: tuple index out of range\n']

## Examples of Using `TracebackException`

With the helper class, we have more options:

    >>> import sys
    >>> from traceback import TracebackException
    >>>
    >>> def lumberjack():
    ...     bright_side_of_life()
    ...
    >>> def bright_side_of_life():
    ...     t = "bright", "side", "of", "life"
    ...     return t[5]
    ...
    >>> try:
    ...     lumberjack()
    ... except IndexError as e:
    ...     exc = e
    ...
    >>> try:
    ...     try:
    ...         lumberjack()
    ...     except:
    ...         1/0
    ... except Exception as e:
    ...     chained_exc = e
    ...
    >>> # limit works as with the module-level functions
    >>> TracebackException.from_exception(exc, limit=-2).print()
    Traceback (most recent call last):
      File "<python-input-1>", line 6, in lumberjack
        bright_side_of_life()
        ~~~~~~~~~~~~~~~~~~~^^
      File "<python-input-1>", line 10, in bright_side_of_life
        return t[5]
               ~^^^
    IndexError: tuple index out of range

    >>> # capture_locals adds local variables in frames
    >>> TracebackException.from_exception(exc, limit=-2, capture_locals=True).print()
    Traceback (most recent call last):
      File "<python-input-1>", line 6, in lumberjack
        bright_side_of_life()
        ~~~~~~~~~~~~~~~~~~~^^
      File "<python-input-1>", line 10, in bright_side_of_life
        return t[5]
               ~^^^
        t = ("bright", "side", "of", "life")
    IndexError: tuple index out of range

    >>> # The *chain* kwarg to print() controls whether chained
    >>> # exceptions are displayed
    >>> TracebackException.from_exception(chained_exc).print()
    Traceback (most recent call last):
      File "<python-input-19>", line 4, in <module>
        lumberjack()
        ~~~~~~~~~~^^
      File "<python-input-8>", line 7, in lumberjack
        bright_side_of_life()
        ~~~~~~~~~~~~~~~~~~~^^
      File "<python-input-8>", line 11, in bright_side_of_life
        return t[5]
               ~^^^
    IndexError: tuple index out of range

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "<python-input-19>", line 6, in <module>
        1/0
        ~^~
    ZeroDivisionError: division by zero

    >>> TracebackException.from_exception(chained_exc).print(chain=False)
    Traceback (most recent call last):
      File "<python-input-19>", line 6, in <module>
        1/0
        ~^~
    ZeroDivisionError: division by zero