72 lines
2.7 KiB
Python
72 lines
2.7 KiB
Python
"""Defines a safe repr function. This will always return a string of "reasonable" length
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no matter what the object does in it's own repr function. Let's examine what can go wrong
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in an arbitrary repr function.
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The default repr will return something like (on Win32 anyway):
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<foo.bar object at 0x008D5650>. Well behaved user-defined repr() methods will do similar.
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The usual expectation is that repr will return a single line string.
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1. However, the repr method can raise an exception of an arbitrary type.
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Also, the return value may not be as expected:
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2. The return value may not be a string!
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3. The return value may not be a single line string, it may contain line breaks.
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4. The method may enter a loop and never return.
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5. The return value may be enormous, eg range(100000)
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The standard library has a nice implementation in the repr module that will do the job,
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but the exception
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handling is silent, so the the output contains no clue that repr() call raised an
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exception. I would like to be told if repr raises an exception, it's a serious error, so
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a sublass of repr overrides the method that does repr for class instances."""
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import repr
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import __builtin__
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class SafeRepr(repr.Repr):
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def __init__(self, *args, **kwargs):
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repr.Repr.__init__(self, *args, **kwargs)
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# Do we need a commandline switch for this?
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self.maxstring = 240 # 3 * 80 chars
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self.maxother = 160 # 2 * 80 chars
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def repr(self, x):
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return self._callhelper(repr.Repr.repr, self, x)
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def repr_instance(self, x, level):
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return self._callhelper(__builtin__.repr, x)
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def _callhelper(self, call, x, *args):
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try:
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# Try the vanilla repr and make sure that the result is a string
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s = call(x, *args)
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except (KeyboardInterrupt, MemoryError, SystemExit):
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raise
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except Exception ,e:
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try:
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exc_name = e.__class__.__name__
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except:
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exc_name = 'unknown'
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try:
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exc_info = str(e)
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except:
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exc_info = 'unknown'
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return '<[%s("%s") raised in repr()] %s object at 0x%x>' % \
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(exc_name, exc_info, x.__class__.__name__, id(x))
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except:
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try:
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name = x.__class__.__name__
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except:
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name = 'unknown'
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return '<[unknown exception raised in repr()] %s object at 0x%x>' % \
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(name, id(x))
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if len(s) > self.maxstring:
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i = max(0, (self.maxstring-3)//2)
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j = max(0, self.maxstring-3-i)
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s = s[:i] + '...' + s[len(s)-j:]
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return s
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_repr = SafeRepr().repr
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