`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)¶: Esto es un atajo para print_exception(sys.exception(), limit, file, chain).

traceback.print_last(limit=None, file=None, chain=True)¶: Esto es un atajo para print_exception(sys.last_exc, limit, file, chain). En general, solo funciona después de que una excepción ha alcanzado un prompt interactivo (ver 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.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)¶

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.

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

`traceback` — Print or retrieve a stack traceback¶

Module-Level Functions¶

`TracebackException` Objects¶

`StackSummary` Objects¶

`FrameSummary` Objects¶

Examples of Using the Module-Level Functions¶

Examples of Using `TracebackException`¶

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traceback — Print or retrieve a stack traceback¶

Module-Level Functions¶

TracebackException Objects¶

StackSummary Objects¶

FrameSummary Objects¶

Examples of Using the Module-Level Functions¶

Examples of Using TracebackException¶

`traceback` — Print or retrieve a stack traceback¶

`TracebackException` Objects¶

`StackSummary` Objects¶

`FrameSummary` Objects¶

Examples of Using `TracebackException`¶