traceback --- 列印或取得堆疊回溯 (stack traceback)¶原始碼：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.
也參考
faulthandler 模組Used to dump Python tracebacks explicitly, on a fault, after a timeout, or on a user signal.
pdb 模組Interactive source code debugger for Python programs.
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.
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.
備註
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.
在 3.5 版的變更: 新增負數 limit 的支援。
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 header Traceback (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.
在 3.5 版的變更: The etype argument is ignored and inferred from the type of value.
在 3.10 版的變更: The etype parameter has been renamed to exc and is now positional-only.
This is a shorthand for print_exception(sys.exception(), limit=limit, file=file,
chain=chain).
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).
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().
在 3.5 版的變更: 新增負數 limit 的支援。
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.
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().
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.
Given a list of tuples or FrameSummary objects as returned by
extract_tb() or extract_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 not None.
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.
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 of
BaseExceptionGroup, the nested exceptions are included as
well, recursively, with indentation relative to their nesting depth.
在 3.10 版的變更: The etype parameter has been renamed to exc and is now positional-only.
在 3.11 版的變更: The returned list now includes any
notes attached to the exception.
在 3.13 版的變更: show_group parameter was added.
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 does print_exception().
在 3.5 版的變更: The etype argument is ignored and inferred from the type of value.
在 3.10 版的變更: This function's behavior and signature were modified to match
print_exception().
This is like print_exc(limit) but returns a string instead of printing to
a file.
format_list(extract_tb(tb, limit)) 的簡寫。
format_list(extract_stack(f, limit)) 的簡寫。
Clears the local variables of all the stack frames in a
traceback tb
by calling the clear() method of each
frame object.
在 3.4 版被加入.
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().
在 3.5 版被加入.
Walk a traceback following tb_next yielding the frame and
line number
for each frame. This helper is used with StackSummary.extract().
在 3.5 版被加入.
TracebackException 物件¶在 3.5 版被加入.
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.
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.
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.
在 3.10 版的變更: 新增 compact 參數。
在 3.11 版的變更: 新增 max_group_width 和 max_group_depth 參數。
A TracebackException of the original
__context__.
If self represents an ExceptionGroup, this field holds a list of
TracebackException instances representing the nested exceptions.
Otherwise it is None.
在 3.11 版被加入.
The __suppress_context__ value from the original
exception.
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.
在 3.11 版被加入.
A StackSummary representing the traceback.
The class of the original traceback.
在 3.13 版之後被棄用.
String display of the class of the original exception.
在 3.13 版被加入.
For syntax errors - the file name where the error occurred.
For syntax errors - the line number where the error occurred.
For syntax errors - the end line number where the error occurred.
Can be None if not present.
在 3.10 版被加入.
For syntax errors - the text where the error occurred.
For syntax errors - the offset into the text where the error occurred.
For syntax errors - the end offset into the text where the error occurred.
Can be None if not present.
在 3.10 版被加入.
For syntax errors - the compiler error message.
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 to file (default sys.stderr) the exception information returned by
format().
在 3.11 版被加入.
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 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, for SyntaxError 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 of
BaseExceptionGroup, the nested exceptions are included as
well, recursively, with indentation relative to their nesting depth.
在 3.11 版的變更: The exception's notes are now
included in the output.
在 3.13 版的變更: 新增 show_group 參數。
StackSummary 物件¶在 3.5 版被加入.
StackSummary objects represent a call stack ready for formatting.
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.
在 3.12 版的變更: Exceptions raised from repr() on a local variable (when
capture_locals is True) are no longer propagated to the caller.
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.
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.
在 3.6 版的變更: Long sequences of repeated frames are now abbreviated.
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.
在 3.11 版被加入.
FrameSummary 物件¶在 3.5 版被加入.
A FrameSummary object represents a single frame
in a traceback.
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
mapping, and if supplied the variable representations are stored in the
summary for later display.
FrameSummary instances have the following attributes:
The filename of the source code for this frame. Equivalent to accessing
f.f_code.co_filename on a
frame object f.
The line number of the source code for this frame.
Equivalent to accessing f.f_code.co_name on
a frame object f.
A string representing the source code for this frame, with leading and
trailing whitespace stripped.
If the source is not available, it is None.
The last line number of the source code for this frame.
By default, it is set to lineno and indexation starts from 1.
在 3.13 版的變更: The default value changed from None to lineno.
The column number of the source code for this frame.
By default, it is None and indexation starts from 0.
The last column number of the source code for this frame.
By default, it is None and indexation starts from 0.
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 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)
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(an_error)
['IndexError: tuple index out of range\n']
TracebackException 的使用範例¶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