pdb "args" crashes when an arg is not printable #65052
Comments
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The "args" command in pdb crashes when an argument cannot be printed. For version 3.3.3: |
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Why is the object not printable? Can you provide a reproducer? Also, the bare except is buggy, it would catch things like KeyboardInterrupt that should not be caught there. 'except Exception' would be appropriate in this case. |
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Thanks for your reaction. |
Oops. Here the correct example:
>>> class foo:
... def __init__(self):
... foo.bar = "hello"
... def __repr__(self): return foo.bar
...
>>> pdb.runcall(foo)
> <stdin>(3)__init__()
(Pdb) a
Traceback (most recent call last):
File ".\pdb.py", line 1132, in do_args
self.message('%s = %r' % (name, dict[name]))
File "<stdin>", line 4, in __repr__
AttributeError: type object 'foo' has no attribute 'bar'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".\pdb.py", line 1580, in runcall
return Pdb().runcall(*args, **kwds)
File "C:\Python33\lib\bdb.py", line 439, in runcall
res = func(*args, **kwds)
File "<stdin>", line 3, in __init__
File "<stdin>", line 3, in __init__
File "C:\Python33\lib\bdb.py", line 47, in trace_dispatch
return self.dispatch_line(frame)
File "C:\Python33\lib\bdb.py", line 65, in dispatch_line
self.user_line(frame)
File ".\pdb.py", line 266, in user_line
self.interaction(frame, None)
File ".\pdb.py", line 345, in interaction
self._cmdloop()
File ".\pdb.py", line 318, in _cmdloop
self.cmdloop()
File "C:\Python33\lib\cmd.py", line 138, in cmdloop
stop = self.onecmd(line)
File ".\pdb.py", line 411, in onecmd
return cmd.Cmd.onecmd(self, line)
File "C:\Python33\lib\cmd.py", line 217, in onecmd
return func(arg)
File ".\pdb.py", line 1134, in do_args
self.message('%s = *** repr failed: %s ***' % (name,))
TypeError: not enough arguments for format stringAt least, I expect pdb to not crash, but a clearer error (as in the patch) is nice to have. |
I am not good at this. Sorry for the mess.
Here is a good example, and a good patch:
>>> class foo:
... def __init__(self):
... foo.bar = "hello"
... def __repr__(self): return foo.bar
...
>>> pdb.runcall(foo)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'pdb' is not defined
>>> import pdb
>>> pdb.runcall(foo)
> <stdin>(3)__init__()
(Pdb) a
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Python33\lib\pdb.py", line 1577, in runcall
return Pdb().runcall(*args, **kwds)
File "C:\Python33\lib\bdb.py", line 439, in runcall
res = func(*args, **kwds)
File "<stdin>", line 3, in __init__
File "<stdin>", line 3, in __init__
File "C:\Python33\lib\bdb.py", line 47, in trace_dispatch
return self.dispatch_line(frame)
File "C:\Python33\lib\bdb.py", line 65, in dispatch_line
self.user_line(frame)
File "C:\Python33\lib\pdb.py", line 266, in user_line
self.interaction(frame, None)
File "C:\Python33\lib\pdb.py", line 345, in interaction
self._cmdloop()
File "C:\Python33\lib\pdb.py", line 318, in _cmdloop
self.cmdloop()
File "C:\Python33\lib\cmd.py", line 138, in cmdloop
stop = self.onecmd(line)
File "C:\Python33\lib\pdb.py", line 411, in onecmd
return cmd.Cmd.onecmd(self, line)
File "C:\Python33\lib\cmd.py", line 217, in onecmd
return func(arg)
File "C:\Python33\lib\pdb.py", line 1131, in do_args
self.message('%s = %r' % (name, dict[name]))
File "<stdin>", line 4, in __repr__
AttributeError: type object 'foo' has no attribute 'bar' |
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There is at least one other place (do_break) where this same problem could crop up. Unittest handles this by having a 'safe_repr' function. pdb doesn't need the same function unittest does, but it could do something similar, and then use %s and this function in the places where it currently uses repr to print an arbitrary object: def safe_repr(obj):
try:
return repr(obj)
except Exception:
return object.__repr__(obj) |
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Maybe we could use Pdb._getval_except(arg, frame=None) in the routine do_args. |
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I did figure it out. At it works perfectly, except for this little surprise:
>>> bar = "BAR"
>>> def foo(bar):
... del bar
... return 5
>>> pdb.runcall(f, 10)
> <stdin>(2)f()
-> del bar
(Pdb) a
bar = 5
(Pdb) n
> <stdin>(3)f()
-> return 5
(Pdb) a
bar = 'BAR' ##### Huh? Expected undefinedI'll leave it to the experts to patch this in proper Python coding style. I did not find a good supporting routine for that elsewhere in pdb. |
Also in do_retval. And the exception is silently ignored in do_p and do_pp when repr() fails, which is not correct. A solution could be to have a message_safe method to be used in such cases. For example, substitute in do_args: self.message('%s = %r' % (name, dict[name]))
with:
self.message_safe('%s = %r', name, dict[name])
def message_safe(self, fmt, *args):
try:
print(fmt % args, file=self.stdout)
except Exception:
exc_info = sys.exc_info()[:2]
self.error(traceback.format_exception_only(*exc_info)[-1].strip()) |
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Commands that silently fail when an object is not printable: p, pp The attached script illustrates all these cases. |
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p/pp commands were fixed in this commit: |
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args, retval and display fixed in #110578, close issue. |
…cts (pythonGH-110578) (cherry picked from commit c523ce0) Co-authored-by: Tian Gao <gaogaotiantian@hotmail.com>
…ay objects (pythonGH-110578) (cherry picked from commit c523ce0) Co-authored-by: Tian Gao <gaogaotiantian@hotmail.com>
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