Lib/traceback.py

   1 """Extract, format and print information about Python stack traces."""
   2
   3 import linecache
   4 import sys
   5 import types
   6
   7 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
   8            'format_exception_only', 'format_list', 'format_stack',
   9            'format_tb', 'print_exc', 'format_exc', 'print_exception',
  10            'print_last', 'print_stack', 'print_tb', 'tb_lineno']
  11
  12 def _print(file, str='', terminator='\n'):
  13     file.write(str+terminator)
  14
  15
  16 def print_list(extracted_list, file=None):
  17     """Print the list of tuples as returned by extract_tb() or
  18     extract_stack() as a formatted stack trace to the given file."""
  19     if file is None:
  20         file = sys.stderr
  21     for filename, lineno, name, line in extracted_list:
  22         _print(file,
  23                '  File "%s", line %d, in %s' % (filename,lineno,name))
  24         if line:
  25             _print(file, '    %s' % line.strip())
  26
  27 def format_list(extracted_list):
  28     """Format a list of traceback entry tuples for printing.
  29
  30     Given a list of tuples as returned by extract_tb() or
  31     extract_stack(), return a list of strings ready for printing.
  32     Each string in the resulting list corresponds to the item with the
  33     same index in the argument list.  Each string ends in a newline;
  34     the strings may contain internal newlines as well, for those items
  35     whose source text line is not None.
  36     """
  37     list = []
  38     for filename, lineno, name, line in extracted_list:
  39         item = '  File "%s", line %d, in %s\n' % (filename,lineno,name)
  40         if line:
  41             item = item + '    %s\n' % line.strip()
  42         list.append(item)
  43     return list
  44
  45
  46 def print_tb(tb, limit=None, file=None):
  47     """Print up to 'limit' stack trace entries from the traceback 'tb'.
  48
  49     If 'limit' is omitted or None, all entries are printed.  If 'file'
  50     is omitted or None, the output goes to sys.stderr; otherwise
  51     'file' should be an open file or file-like object with a write()
  52     method.
  53     """
  54     if file is None:
  55         file = sys.stderr
  56     if limit is None:
  57         if hasattr(sys, 'tracebacklimit'):
  58             limit = sys.tracebacklimit
  59     n = 0
  60     while tb is not None and (limit is None or n < limit):
  61         f = tb.tb_frame
  62         lineno = tb.tb_lineno
  63         co = f.f_code
  64         filename = co.co_filename
  65         name = co.co_name
  66         _print(file,
  67                '  File "%s", line %d, in %s' % (filename,lineno,name))
  68         linecache.checkcache(filename)
  69         line = linecache.getline(filename, lineno)
  70         if line: _print(file, '    ' + line.strip())
  71         tb = tb.tb_next
  72         n = n+1
  73
  74 def format_tb(tb, limit = None):
  75     """A shorthand for 'format_list(extract_stack(f, limit))."""
  76     return format_list(extract_tb(tb, limit))
  77
  78 def extract_tb(tb, limit = None):
  79     """Return list of up to limit pre-processed entries from traceback.
  80
  81     This is useful for alternate formatting of stack traces.  If
  82     'limit' is omitted or None, all entries are extracted.  A
  83     pre-processed stack trace entry is a quadruple (filename, line
  84     number, function name, text) representing the information that is
  85     usually printed for a stack trace.  The text is a string with
  86     leading and trailing whitespace stripped; if the source is not
  87     available it is None.
  88     """
  89     if limit is None:
  90         if hasattr(sys, 'tracebacklimit'):
  91             limit = sys.tracebacklimit
  92     list = []
  93     n = 0
  94     while tb is not None and (limit is None or n < limit):
  95         f = tb.tb_frame
  96         lineno = tb.tb_lineno
  97         co = f.f_code
  98         filename = co.co_filename
  99         name = co.co_name
 100         linecache.checkcache(filename)
 101         line = linecache.getline(filename, lineno)
 102         if line: line = line.strip()
 103         else: line = None
 104         list.append((filename, lineno, name, line))
 105         tb = tb.tb_next
 106         n = n+1
 107     return list
 108
 109
 110 def print_exception(etype, value, tb, limit=None, file=None):
 111     """Print exception up to 'limit' stack trace entries from 'tb' to 'file'.
 112
 113     This differs from print_tb() in the following ways: (1) if
 114     traceback is not None, it prints a header "Traceback (most recent
 115     call last):"; (2) it prints the exception type and value after the
 116     stack trace; (3) if type is SyntaxError and value has the
 117     appropriate format, it prints the line where the syntax error
 118     occurred with a caret on the next line indicating the approximate
 119     position of the error.
 120     """
 121     if file is None:
 122         file = sys.stderr
 123     if tb:
 124         _print(file, 'Traceback (most recent call last):')
 125         print_tb(tb, limit, file)
 126     lines = format_exception_only(etype, value)
 127     for line in lines[:-1]:
 128         _print(file, line, ' ')
 129     _print(file, lines[-1], '')
 130
 131 def format_exception(etype, value, tb, limit = None):
 132     """Format a stack trace and the exception information.
 133
 134     The arguments have the same meaning as the corresponding arguments
 135     to print_exception().  The return value is a list of strings, each
 136     ending in a newline and some containing internal newlines.  When
 137     these lines are concatenated and printed, exactly the same text is
 138     printed as does print_exception().
 139     """
 140     if tb:
 141         list = ['Traceback (most recent call last):\n']
 142         list = list + format_tb(tb, limit)
 143     else:
 144         list = []
 145     list = list + format_exception_only(etype, value)
 146     return list
 147
 148 def format_exception_only(etype, value):
 149     """Format the exception part of a traceback.
 150
 151     The arguments are the exception type and value such as given by
 152     sys.last_type and sys.last_value. The return value is a list of
 153     strings, each ending in a newline.  Normally, the list contains a
 154     single string; however, for SyntaxError exceptions, it contains
 155     several lines that (when printed) display detailed information
 156     about where the syntax error occurred.  The message indicating
 157     which exception occurred is the always last string in the list.
 158     """
 159     list = []
 160     if (type(etype) == types.ClassType
 161         or issubclass(etype, Exception)):
 162         stype = etype.__name__
 163     else:
 164         stype = etype
 165     if value is None:
 166         list.append(str(stype) + '\n')
 167     else:
 168         if etype is SyntaxError:
 169             try:
 170                 msg, (filename, lineno, offset, line) = value
 171             except:
 172                 pass
 173             else:
 174                 if not filename: filename = "<string>"
 175                 list.append('  File "%s", line %d\n' %
 176                             (filename, lineno))
 177                 if line is not None:
 178                     i = 0
 179                     while i < len(line) and line[i].isspace():
 180                         i = i+1
 181                     list.append('    %s\n' % line.strip())
 182                     if offset is not None:
 183                         s = '    '
 184                         for c in line[i:offset-1]:
 185                             if c.isspace():
 186                                 s = s + c
 187                             else:
 188                                 s = s + ' '
 189                         list.append('%s^\n' % s)
 190                     value = msg
 191         s = _some_str(value)
 192         if s:
 193             list.append('%s: %s\n' % (str(stype), s))
 194         else:
 195             list.append('%s\n' % str(stype))
 196     return list
 197
 198 def _some_str(value):
 199     try:
 200         return str(value)
 201     except:
 202         return '<unprintable %s object>' % type(value).__name__
 203
 204
 205 def print_exc(limit=None, file=None):
 206     """Shorthand for 'print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)'.
 207     (In fact, it uses sys.exc_info() to retrieve the same information
 208     in a thread-safe way.)"""
 209     if file is None:
 210         file = sys.stderr
 211     try:
 212         etype, value, tb = sys.exc_info()
 213         print_exception(etype, value, tb, limit, file)
 214     finally:
 215         etype = value = tb = None
 216
 217
 218 def format_exc(limit=None):
 219     """Like print_exc() but return a string."""
 220     try:
 221         etype, value, tb = sys.exc_info()
 222         return ''.join(format_exception(etype, value, tb, limit))
 223     finally:
 224         etype = value = tb = None
 225
 226
 227 def print_last(limit=None, file=None):
 228     """This is a shorthand for 'print_exception(sys.last_type,
 229     sys.last_value, sys.last_traceback, limit, file)'."""
 230     if file is None:
 231         file = sys.stderr
 232     print_exception(sys.last_type, sys.last_value, sys.last_traceback,
 233                     limit, file)
 234
 235
 236 def print_stack(f=None, limit=None, file=None):
 237     """Print a stack trace from its invocation point.
 238
 239     The optional 'f' argument can be used to specify an alternate
 240     stack frame at which to start. The optional 'limit' and 'file'
 241     arguments have the same meaning as for print_exception().
 242     """
 243     if f is None:
 244         try:
 245             raise ZeroDivisionError
 246         except ZeroDivisionError:
 247             f = sys.exc_info()[2].tb_frame.f_back
 248     print_list(extract_stack(f, limit), file)
 249
 250 def format_stack(f=None, limit=None):
 251     """Shorthand for 'format_list(extract_stack(f, limit))'."""
 252     if f is None:
 253         try:
 254             raise ZeroDivisionError
 255         except ZeroDivisionError:
 256             f = sys.exc_info()[2].tb_frame.f_back
 257     return format_list(extract_stack(f, limit))
 258
 259 def extract_stack(f=None, limit = None):
 260     """Extract the raw traceback from the current stack frame.
 261
 262     The return value has the same format as for extract_tb().  The
 263     optional 'f' and 'limit' arguments have the same meaning as for
 264     print_stack().  Each item in the list is a quadruple (filename,
 265     line number, function name, text), and the entries are in order
 266     from oldest to newest stack frame.
 267     """
 268     if f is None:
 269         try:
 270             raise ZeroDivisionError
 271         except ZeroDivisionError:
 272             f = sys.exc_info()[2].tb_frame.f_back
 273     if limit is None:
 274         if hasattr(sys, 'tracebacklimit'):
 275             limit = sys.tracebacklimit
 276     list = []
 277     n = 0
 278     while f is not None and (limit is None or n < limit):
 279         lineno = f.f_lineno
 280         co = f.f_code
 281         filename = co.co_filename
 282         name = co.co_name
 283         linecache.checkcache(filename)
 284         line = linecache.getline(filename, lineno)
 285         if line: line = line.strip()
 286         else: line = None
 287         list.append((filename, lineno, name, line))
 288         f = f.f_back
 289         n = n+1
 290     list.reverse()
 291     return list
 292
 293 def tb_lineno(tb):
 294     """Calculate correct line number of traceback given in tb.
 295
 296     Obsolete in 2.3.
 297     """
 298     return tb.tb_lineno