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1# Copyright 2014 The Chromium Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4
5"""Print prettier and more detailed exceptions."""
6
7import logging
8import math
9import os
10import sys
11import traceback
12
13from telemetry.core import exceptions
14
15
16def PrintFormattedException(exception_class=None, exception=None, tb=None,
17                            msg=None):
18  logging.info('Try printing formatted exception: %s %s %s' %
19               (exception_class, exception, tb))
20  assert bool(exception_class) == bool(exception) == bool(tb), (
21      'Must specify all or none of exception_class, exception, and tb')
22
23  if not exception_class:
24    exception_class, exception, tb = sys.exc_info()
25
26  if exception_class == exceptions.IntentionalException:
27    return
28
29  def _GetFinalFrame(tb_level):
30    while tb_level.tb_next:
31      tb_level = tb_level.tb_next
32    return tb_level.tb_frame
33
34  processed_tb = traceback.extract_tb(tb)
35  frame = _GetFinalFrame(tb)
36  exception_list = traceback.format_exception_only(exception_class, exception)
37  exception_string = '\n'.join(l.strip() for l in exception_list)
38
39  if msg:
40    print >> sys.stderr
41    print >> sys.stderr, msg
42
43  _PrintFormattedTrace(processed_tb, frame, exception_string)
44
45
46def PrintFormattedFrame(frame, exception_string=None):
47  _PrintFormattedTrace(traceback.extract_stack(frame), frame, exception_string)
48
49
50def _PrintFormattedTrace(processed_tb, frame, exception_string=None):
51  """Prints an Exception in a more useful format than the default.
52
53  TODO(tonyg): Consider further enhancements. For instance:
54    - Report stacks to maintainers like depot_tools does.
55    - Add a debug flag to automatically start pdb upon exception.
56  """
57  print >> sys.stderr
58
59  # Format the traceback.
60  print >> sys.stderr, 'Traceback (most recent call last):'
61  for filename, line, function, text in processed_tb:
62    filename = os.path.abspath(filename)
63    print >> sys.stderr, '  %s at %s:%d' % (function, filename, line)
64    print >> sys.stderr, '    %s' % text
65
66  # Format the exception.
67  if exception_string:
68    print >> sys.stderr, exception_string
69
70  # Format the locals.
71  local_variables = [(variable, value) for variable, value in
72                     frame.f_locals.iteritems() if variable != 'self']
73  print >> sys.stderr
74  print >> sys.stderr, 'Locals:'
75  if local_variables:
76    longest_variable = max(len(v) for v, _ in local_variables)
77    for variable, value in sorted(local_variables):
78      value = repr(value)
79      possibly_truncated_value = _AbbreviateMiddleOfString(value, ' ... ', 1024)
80      truncation_indication = ''
81      if len(possibly_truncated_value) != len(value):
82        truncation_indication = ' (truncated)'
83      print >> sys.stderr, '  %s: %s%s' % (variable.ljust(longest_variable + 1),
84                                           possibly_truncated_value,
85                                           truncation_indication)
86  else:
87    print >> sys.stderr, '  No locals!'
88
89  print >> sys.stderr
90  sys.stderr.flush()
91
92
93def _AbbreviateMiddleOfString(target, middle, max_length):
94  if max_length < 0:
95    raise ValueError('Must provide positive max_length')
96  if len(middle) > max_length:
97    raise ValueError('middle must not be greater than max_length')
98
99  if len(target) <= max_length:
100    return target
101  half_length = (max_length - len(middle)) / 2.
102  return (target[:int(math.floor(half_length))] + middle +
103          target[-int(math.ceil(half_length)):])
104