Lib/traceback.py

"""Extract, format and print information about Python stack traces."""

import linecache
import sys
import types

__all__ = ['extract_stack', 'extract_tb', 'format_exception',
           'format_exception_only', 'format_list', 'format_stack',
           'format_tb', 'print_exc', 'print_exception', 'print_last',
           'print_stack', 'print_tb', 'tb_lineno']

def _print(file, str='', terminator='\n'):
    file.write(str+terminator)


def 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 not file:
        file = sys.stderr
    for filename, lineno, name, line in extracted_list:
        _print(file,
               '  File "%s", line %d, in %s' % (filename,lineno,name))
        if line:
            _print(file, '    %s' % line.strip())

def format_list(extracted_list):
    """Given a list of tuples 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."""
    list = []
    for filename, lineno, name, line in extracted_list:
        item = '  File "%s", line %d, in %s\n' % (filename,lineno,name)
        if line:
            item = item + '    %s\n' % line.strip()
        list.append(item)
    return list


def print_tb(tb, limit=None, file=None):
    """Print up to 'limit' stack trace entries from the traceback 'tb'.
    If 'limit' is omitted or None, all entries are printed.  If 'file' is
    omitted or None, the output goes to sys.stderr; otherwise 'file'
    should be an open file or file-like object with a write() method."""
    if not file:
        file = sys.stderr
    if limit is None:
        if hasattr(sys, 'tracebacklimit'):
            limit = sys.tracebacklimit
    n = 0
    while tb is not None and (limit is None or n < limit):
        f = tb.tb_frame
        lineno = tb_lineno(tb)
        co = f.f_code
        filename = co.co_filename
        name = co.co_name
        _print(file,
               '  File "%s", line %d, in %s' % (filename,lineno,name))
        line = linecache.getline(filename, lineno)
        if line: _print(file, '    ' + line.strip())
        tb = tb.tb_next
        n = n+1

def format_tb(tb, limit = None):
    """A shorthand for 'format_list(extract_stack(f, limit))."""
    return format_list(extract_tb(tb, limit))

def extract_tb(tb, limit = None):
    """Return a list of up to 'limit' pre-processed stack trace entries
    extracted from the traceback object 'traceback'.  This is useful for
    alternate formatting of stack traces.  If 'limit' is omitted or None,
    all entries are extracted.  A pre-processed stack trace entry is a
    quadruple (filename, line number, function name, text) representing
    the information that is usually printed for a stack trace.  The text
    is a string with leading and trailing whitespace stripped; if the
    source is not available it is None."""
    if limit is None:
        if hasattr(sys, 'tracebacklimit'):
            limit = sys.tracebacklimit
    list = []
    n = 0
    while tb is not None and (limit is None or n < limit):
        f = tb.tb_frame
        lineno = tb_lineno(tb)
        co = f.f_code
        filename = co.co_filename
        name = co.co_name
        line = linecache.getline(filename, lineno)
        if line: line = line.strip()
        else: line = None
        list.append((filename, lineno, name, line))
        tb = tb.tb_next
        n = n+1
    return list


def print_exception(etype, value, tb, limit=None, file=None):
    """Print exception information and up to 'limit' stack trace entries
    from the traceback 'tb' to 'file'.  This differs from print_tb() in
    the following ways: (1) if traceback is not None, it prints a header
    "Traceback (most recent call last):"; (2) it prints the exception type and
    value after the stack trace; (3) if type is SyntaxError and value has
    the appropriate format, it prints the line where the syntax error
    occurred with a caret on the next line indicating the approximate
    position of the error."""
    if not file:
        file = sys.stderr
    if tb:
        _print(file, 'Traceback (most recent call last):')
        print_tb(tb, limit, file)
    lines = format_exception_only(etype, value)
    for line in lines[:-1]:
        _print(file, line, ' ')
    _print(file, lines[-1], '')

def format_exception(etype, value, tb, limit = None):
    """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()."""
    if tb:
        list = ['Traceback (most recent call last):\n']
        list = list + format_tb(tb, limit)
    else:
        list = []
    list = list + format_exception_only(etype, value)
    return list

def format_exception_only(etype, value):
    """Format the exception part of a traceback.  The arguments are the
    exception type and value such as given by sys.last_type and
    sys.last_value. The return value is a list of strings, each ending
    in a newline.  Normally, the list contains a single string;
    however, for SyntaxError exceptions, it contains several lines that
    (when printed) display detailed information about where the syntax
    error occurred.  The message indicating which exception occurred is
    the always last string in the list."""
    list = []
    if type(etype) == types.ClassType:
        stype = etype.__name__
    else:
        stype = etype
    if value is None:
        list.append(str(stype) + '\n')
    else:
        if etype is SyntaxError:
            try:
                msg, (filename, lineno, offset, line) = value
            except:
                pass
            else:
                if not filename: filename = "<string>"
                list.append('  File "%s", line %d\n' %
                            (filename, lineno))
                i = 0
                while i < len(line) and line[i].isspace():
                    i = i+1
                list.append('    %s\n' % line.strip())
                s = '    '
                for c in line[i:offset-1]:
                    if c.isspace():
                        s = s + c
                    else:
                        s = s + ' '
                list.append('%s^\n' % s)
                value = msg
        s = _some_str(value)
        if s:
            list.append('%s: %s\n' % (str(stype), s))
        else:
            list.append('%s\n' % str(stype))
    return list

def _some_str(value):
    try:
        return str(value)
    except:
        return '<unprintable %s object>' % type(value).__name__


def print_exc(limit=None, file=None):
    """This is a shorthand for 'print_exception(sys.exc_type,
    sys.exc_value, sys.exc_traceback, limit, file)'.
    (In fact, it uses sys.exc_info() to retrieve the same information
    in a thread-safe way.)"""
    if not file:
        file = sys.stderr
    try:
        etype, value, tb = sys.exc_info()
        print_exception(etype, value, tb, limit, file)
    finally:
        etype = value = tb = None

def print_last(limit=None, file=None):
    """This is a shorthand for 'print_exception(sys.last_type,
    sys.last_value, sys.last_traceback, limit, file)'."""
    if not file:
        file = sys.stderr
    print_exception(sys.last_type, sys.last_value, sys.last_traceback,
                    limit, file)


def print_stack(f=None, limit=None, file=None):
    """This function prints a stack trace from its invocation point.
    The optional 'f' argument can be used to specify an alternate stack
    frame at which to start. The optional 'limit' and 'file' arguments
    have the same meaning as for print_exception()."""
    if f is None:
        try:
            raise ZeroDivisionError
        except ZeroDivisionError:
            f = sys.exc_info()[2].tb_frame.f_back
    print_list(extract_stack(f, limit), file)

def format_stack(f=None, limit=None):
    """A shorthand for 'format_list(extract_stack(f, limit))'."""
    if f is None:
        try:
            raise ZeroDivisionError
        except ZeroDivisionError:
            f = sys.exc_info()[2].tb_frame.f_back
    return format_list(extract_stack(f, limit))

def 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().
    Each item in the list is a quadruple (filename, line number,
    function name, text), and the entries are in order from oldest
    to newest stack frame."""
    if f is None:
        try:
            raise ZeroDivisionError
        except ZeroDivisionError:
            f = sys.exc_info()[2].tb_frame.f_back
    if limit is None:
        if hasattr(sys, 'tracebacklimit'):
            limit = sys.tracebacklimit
    list = []
    n = 0
    while f is not None and (limit is None or n < limit):
        lineno = f.f_lineno     # XXX Too bad if -O is used
        co = f.f_code
        filename = co.co_filename
        name = co.co_name
        line = linecache.getline(filename, lineno)
        if line: line = line.strip()
        else: line = None
        list.append((filename, lineno, name, line))
        f = f.f_back
        n = n+1
    list.reverse()
    return list

def tb_lineno(tb):
    """Calculate the correct line number of the traceback given in tb
    (even with -O on)."""

    # Coded by Marc-Andre Lemburg from the example of PyCode_Addr2Line()
    # in compile.c.
    # Revised version by Jim Hugunin to work with JPython too.

    c = tb.tb_frame.f_code
    if not hasattr(c, 'co_lnotab'):
        return tb.tb_lineno

    tab = c.co_lnotab
    line = c.co_firstlineno
    stopat = tb.tb_lasti
    addr = 0
    for i in range(0, len(tab), 2):
        addr = addr + ord(tab[i])
        if addr > stopat:
            break
        line = line + ord(tab[i+1])
    return line