traceback --- 列印或取得堆疊回溯 (stack traceback)

原始碼：Lib/traceback.py

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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.

在 3.13 版被加入: Output is colorized by default and can be controlled using environment variables.

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.

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。

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 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.

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().

在 3.5 版的變更: 新增負數 limit 的支援。

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)

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.

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, 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: 新增 show_group 參數。

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 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().

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)

format_list(extract_tb(tb, limit)) 的簡寫。

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

format_list(extract_stack(f, limit)) 的簡寫。

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.

在 3.4 版被加入.

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().

在 3.5 版被加入.

在 3.14 版的變更: This function previously returned a generator that would walk the stack when first iterated over. The generator returned now is the state of the stack when walk_stack is called.

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().

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.

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.

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。

__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.

在 3.11 版被加入.

__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.

在 3.11 版被加入.

stack

A StackSummary representing the traceback.

exc_type

The class of the original traceback.

在 3.13 版之後被棄用.

exc_type_str

String display of the class of the original exception.

在 3.13 版被加入.

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.

在 3.10 版被加入.

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.

在 3.10 版被加入.

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 by format().

在 3.11 版被加入.

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, 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.

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.

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.

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.

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.

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.

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.

class traceback.FrameSummary(filename, lineno, name, *, lookup_line=True, locals=None,