traceback
--- Print or retrieve a stack traceback¶
Source code: Lib/traceback.py
This module provides a standard interface to extract, format and print stack traces of Python programs. It exactly mimics the behavior of the Python interpreter when it prints a stack trace. This is useful when you want to print stack traces under program control, such as in a "wrapper" around the interpreter.
The module uses traceback objects --- these are
objects of type types.TracebackType
,
which are assigned to the __traceback__
field of
BaseException
instances.
Voir aussi
- Module
faulthandler
Used to dump Python tracebacks explicitly, on a fault, after a timeout, or on a user signal.
- Module
pdb
Interactive source code debugger for Python programs.
Le module définit les fonctions suivantes :
- 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 orNone
, all entries are printed. If file is omitted orNone
, the output goes tosys.stderr
; otherwise it should be an open file or file-like object to receive the output.Note
The meaning of the limit parameter is different than the meaning of
sys.tracebacklimit
. A negative limit value corresponds to a positive value ofsys.tracebacklimit
, whereas the behaviour of a positive limit value cannot be achieved withsys.tracebacklimit
.Modifié dans la version 3.5: Added negative limit support.
- 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:if tb is not
None
, it prints a headerTraceback (most recent call last):
it prints the exception type and value after the stack trace
if type(value) is
SyntaxError
and value has the appropriate format, it prints the line where the syntax error occurred with a caret indicating the approximate position of the error.
Since Python 3.10, instead of passing value and tb, an exception object can be passed as the first argument. If value and tb are provided, the first argument is ignored in order to provide backwards compatibility.
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.Modifié dans la version 3.5: The etype argument is ignored and inferred from the type of value.
Modifié dans la version 3.10: The etype parameter has been renamed to exc and is now positional-only.
- traceback.print_exc(limit=None, file=None, chain=True)¶
This is a shorthand for
print_exception(sys.exception(), limit, file, chain)
.
- traceback.print_last(limit=None, file=None, chain=True)¶
This is a shorthand for
print_exception(sys.last_exc, limit, file, chain)
. In general it will work only after an exception has reached an interactive prompt (seesys.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 orNone
, 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 forprint_tb()
.Modifié dans la version 3.5: Added negative limit support.
- 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 forprint_tb()
. A "pre-processed" stack trace entry is aFrameSummary
object containing attributesfilename
,lineno
,name
, andline
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 forprint_stack()
.
- traceback.format_list(extracted_list)¶
Given a list of tuples or
FrameSummary
objects as returned byextract_tb()
orextract_stack()
, return a list of strings ready for printing. Each string in the resulting list corresponds to the item with the same index in the argument list. Each string ends in a newline; the strings may contain internal newlines as well, for those items whose source text line is notNone
.
- traceback.format_exception_only(exc, /, [value, ]*, show_group=False)¶
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, forSyntaxError
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'snotes
.Since Python 3.10, instead of passing value, an exception object can be passed as the first argument. If value is provided, the first argument is ignored in order to provide backwards compatibility.
When show_group is
True
, and the exception is an instance ofBaseExceptionGroup
, the nested exceptions are included as well, recursively, with indentation relative to their nesting depth.Modifié dans la version 3.10: The etype parameter has been renamed to exc and is now positional-only.
Modifié dans la version 3.11: The returned list now includes any
notes
attached to the exception.Modifié dans la version 3.13: show_group parameter was added.
- traceback.format_exception(exc, /, [value, tb, ]limit=None, chain=True)¶
Format a stack trace and the exception information. The arguments have the same meaning as the corresponding arguments to
print_exception()
. The return value is a list of strings, each ending in a newline and some containing internal newlines. When these lines are concatenated and printed, exactly the same text is printed as doesprint_exception()
.Modifié dans la version 3.5: The etype argument is ignored and inferred from the type of value.
Modifié dans la version 3.10: This function's behavior and signature were modified to match
print_exception()
.
- traceback.format_exc(limit=None, chain=True)¶
This is like
print_exc(limit)
but returns a string instead of printing to a file.
- traceback.format_tb(tb, limit=None)¶
A shorthand for
format_list(extract_tb(tb, limit))
.
- traceback.format_stack(f=None, limit=None)¶
A shorthand for
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.Ajouté dans la 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 isNone
, the current stack is used. This helper is used withStackSummary.extract()
.Ajouté dans la 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 withStackSummary.extract()
.Ajouté dans la version 3.5.
The module also defines the following classes:
TracebackException
Objects¶
Ajouté dans la version 3.5.
TracebackException
objects are created from actual exceptions to
capture data for later printing in a lightweight fashion.
- 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. limit, lookup_lines and capture_locals are as for the
StackSummary
class.If compact is true, only data that is required by
TracebackException
'sformat()
method is saved in the class attributes. In particular, the__context__
field is calculated only if__cause__
isNone
and__suppress_context__
is false.Note that when locals are captured, they are also shown in the traceback.
max_group_width and max_group_depth control the formatting of exception groups (see
BaseExceptionGroup
). The depth refers to the nesting level of the group, and the width refers to the size of a single exception group's exceptions array. The formatted output is truncated when either limit is exceeded.Modifié dans la version 3.10: Added the compact parameter.
Modifié dans la version 3.11: Added the max_group_width and max_group_depth parameters.
- __context__¶
A
TracebackException
of the original__context__
.
- exceptions¶
If
self
represents anExceptionGroup
, this field holds a list ofTracebackException
instances representing the nested exceptions. Otherwise it isNone
.Ajouté dans la version 3.11.
- __suppress_context__¶
The
__suppress_context__
value from the original exception.
- __notes__¶
The
__notes__
value from the original exception, orNone
if the exception does not have any notes. If it is notNone
is it formatted in the traceback after the exception string.Ajouté dans la version 3.11.
- stack¶
A
StackSummary
representing the traceback.
- exc_type¶
The class of the original traceback.
Obsolète depuis la version 3.13.
- exc_type_str¶
String display of the class of the original exception.
Ajouté dans la version 3.13.
- filename¶
For syntax errors - the file name where the error occurred.
- lineno¶
For syntax errors - the line number where the error occurred.
- end_lineno¶
For syntax errors - the end line number where the error occurred. Can be
None
if not present.Ajouté dans la version 3.10.
- text¶
For syntax errors - the text where the error occurred.
- offset¶
For syntax errors - the offset into the text where the error occurred.
- end_offset¶
For syntax errors - the end offset into the text where the error occurred. Can be
None
if not present.Ajouté dans la version 3.10.
- msg¶
For syntax errors - the compiler error message.
- classmethod from_exception(exc, *, limit=None, lookup_lines=True, capture_locals=False)¶
Capture an exception for later rendering. limit, lookup_lines and capture_locals are as for the
StackSummary
class.Note that when locals are captured, they are also shown in the traceback.
- print(*, file=None, chain=True)¶
Print to file (default
sys.stderr
) the exception information returned byformat()
.Ajouté dans la version 3.11.
- format(*, chain=True)¶
Format the exception.
If chain is not
True
,__cause__
and__context__
will not be formatted.The return value is a generator of strings, each ending in a newline and some containing internal newlines.
print_exception()
is a wrapper around this method which just prints the lines to a file.
- format_exception_only(*, show_group=False)¶
Format the exception part of the traceback.
The return value is a generator of strings, each ending in a newline.
When show_group is
False
, the generator emits the exception's message followed by its notes (if it has any). The exception message is normally a single string; however, forSyntaxError
exceptions, it consists of several lines that (when printed) display detailed information about where the syntax error occurred.When show_group is
True
, and the exception is an instance ofBaseExceptionGroup
, the nested exceptions are included as well, recursively, with indentation relative to their nesting depth.Modifié dans la version 3.11: The exception's
notes
are now included in the output.Modifié dans la version 3.13: Added the show_group parameter.
StackSummary
Objects¶
Ajouté dans la 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 bywalk_stack()
orwalk_tb()
).If limit is supplied, only this many frames are taken from frame_gen. If lookup_lines is
False
, the returnedFrameSummary
objects will not have read their lines in yet, making the cost of creating theStackSummary
cheaper (which may be valuable if it may not actually get formatted). If capture_locals isTrue
the local variables in eachFrameSummary
are captured as object representations.Modifié dans la version 3.12: Exceptions raised from
repr()
on a local variable (when capture_locals isTrue
) are no longer propagated to the caller.
- classmethod from_list(a_list)¶
Construct a
StackSummary
object from a supplied list ofFrameSummary
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.
For long sequences of the same frame and line, the first few repetitions are shown, followed by a summary line stating the exact number of further repetitions.
Modifié dans la version 3.6: Long sequences of repeated frames are now abbreviated.
- 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 byStackSummary.format()
. If it returnsNone
, the frame is omitted from the output.Ajouté dans la version 3.11.
FrameSummary
Objects¶
Ajouté dans la 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 theFrameSummary
has theline
attribute accessed (which also happens when casting it to atuple
).line
may be directly provided, and will prevent line lookups happening at all. locals is an optional local variable mapping, 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
.
Traceback Examples¶
This simple example implements a basic read-eval-print loop, similar to (but
less useful than) the standard Python interactive interpreter loop. For a more
complete implementation of the interpreter loop, refer to the code
module.
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)
The following example demonstrates the different ways to print and format the exception and traceback:
import sys, traceback
def lumberjack():
bright_side_of_life()
def bright_side_of_life():
return tuple()[0]
try:
lumberjack()
except IndexError:
exc = sys.exception()
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)
The output for the example would look similar to this:
*** 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 ~~~~~~~~~~^^\n',
' File "<doctest default[0]>", line 4, in lumberjack\n bright_side_of_life()\n ~~~~~~~~~~~~~~~~~~~^^\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 ~~~~~~~~~~^^\n',
' File "<doctest default[0]>", line 4, in lumberjack\n bright_side_of_life()\n ~~~~~~~~~~~~~~~~~~~^^\n',
' File "<doctest default[0]>", line 7, in bright_side_of_life\n return tuple()[0]\n ~~~~~~~^^^\n']
*** tb_lineno: 10
The following example shows the different ways to print and format the stack:
>>> 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']
This last example demonstrates the final few formatting functions:
>>> 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(type(an_error), an_error)
['IndexError: tuple index out of range\n']