prompt: You will be provided with a partial code base and an issue statement explaining a problem to resolve.
  <issue>
  verifydb fails with debug in some cases
  Using `./bin/instance verifydb -D` to check the `Data.fs` it fails in some cases:
  
  ```
  Traceback (most recent call last):
    File "/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py", line 68, in verify_record
      class_info = unpickler.load()
    File "/Users/pbauer/.cache/buildout/eggs/ZODB-5.5.1-py3.7.egg/ZODB/_compat.py", line 62, in find_class
      return super(Unpickler, self).find_class(modulename, name)
  ModuleNotFoundError: No module named 'Products.Archetypes'
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "./bin/instance", line 262, in <module>
      + sys.argv[1:]))
    File "/Users/pbauer/.cache/buildout/eggs/plone.recipe.zope2instance-6.1.3-py3.7.egg/plone/recipe/zope2instance/ctl.py", line 937, in main
      c.onecmd(' '.join(options.args))
    File "/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/cmd.py", line 217, in onecmd
      return func(arg)
    File "/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py", line 31, in zopectl_entry
      verify_zodb(app, debug=options.debug)
    File "/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py", line 50, in verify_zodb
      success = verify_record(oid, data, debug)
    File "/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py", line 82, in verify_record
      pickletools.dis(pickle[pos:])
  UnboundLocalError: local variable 'pos' referenced before assignment
  ```
  
  </issue>
  <code>
  [start of Products/CMFPlone/_scripts/verifydb.py]
  1 # -*- coding: utf-8 -*-
  2 from Zope2.Startup.run import make_wsgi_app
  3 from ZODB.interfaces import IStorageCurrentRecordIteration
  4 from ZODB.serialize import PersistentUnpickler
  5 
  6 import argparse
  7 import io
  8 import logging
  9 import pdb
  10 import pickletools
  11 import sys
  12 import traceback
  13 import Zope2
  14 
  15 logger = logging.getLogger('zodbverify')
  16 
  17 
  18 def zopectl_entry(self, arg):
  19     parser = argparse.ArgumentParser(
  20         prog=sys.argv[0] + ' verifydb',
  21         description='Verifies that all records in the database can be loaded.',
  22     )
  23     parser.add_argument(
  24         '-D', '--debug', action='store_true', dest='debug',
  25         help='pause to debug broken pickles')
  26     options = parser.parse_args(arg.split(' ') if arg else [])
  27 
  28     logging.basicConfig(level=logging.INFO)
  29     make_wsgi_app({}, self.options.configfile)
  30     app = Zope2.app()
  31     verify_zodb(app, debug=options.debug)
  32 
  33 
  34 def verify_zodb(obj, debug=False):
  35     storage = obj._p_jar._db._storage
  36     if not IStorageCurrentRecordIteration.providedBy(storage):
  37         raise TypeError(
  38             'ZODB storage {} does not implement record_iternext'.format(
  39                 storage))
  40 
  41     logger.info('Scanning ZODB...')
  42 
  43     next_ = None
  44     count = 0
  45     errors = 0
  46     while True:
  47         count += 1
  48         oid, tid, data, next_ = storage.record_iternext(next_)
  49         logger.debug('Verifying {}'.format(oid))
  50         success = verify_record(oid, data, debug)
  51         if not success:
  52             errors += 1
  53         if next_ is None:
  54             break
  55 
  56     logger.info(
  57         'Done! Scanned {} records. '
  58         'Found {} records that could not be loaded.'.format(
  59             count, errors)
  60     )
  61 
  62 
  63 def verify_record(oid, data, debug=False):
  64     input_file = io.BytesIO(data)
  65     unpickler = PersistentUnpickler(None, persistent_load, input_file)
  66     class_info = 'unknown'
  67     try:
  68         class_info = unpickler.load()
  69         pos = input_file.tell()
  70         unpickler.load()
  71     except Exception:
  72         input_file.seek(0)
  73         pickle = input_file.read()
  74         logger.info('\nCould not process {} record {}:'.format(
  75             class_info,
  76             repr(oid),
  77         ))
  78         logger.info(repr(pickle))
  79         logger.info(traceback.format_exc())
  80         if debug:
  81             try:
  82                 pickletools.dis(pickle[pos:])
  83             finally:
  84                 pdb.set_trace()
  85         return False
  86     return True
  87 
  88 
  89 def persistent_load(ref):
  90     pass
  91
  [end of Products/CMFPlone/_scripts/verifydb.py]
  </code>
  
  I need you to solve this issue by generating a single patch file that I can apply directly to this repository using git apply. Please respond with a single patch file in the following format.
  <patch>
  diff --git a/file.py b/file.py
  --- a/file.py
  +++ b/file.py
  @@ -1,27 +1,35 @@
   def euclidean(a, b):
  -    while b:
  -        a, b = b, a % b
  -    return a
  +    if b == 0:
  +        return a
  +    return euclidean(b, a % b)
   
   
   def bresenham(x0, y0, x1, y1):
       points = []
       dx = abs(x1 - x0)
       dy = abs(y1 - y0)
  -    sx = 1 if x0 < x1 else -1
  -    sy = 1 if y0 < y1 else -1
  -    err = dx - dy
  +    x, y = x0, y0
  +    sx = -1 if x0 > x1 else 1
  +    sy = -1 if y0 > y1 else 1
   
  -    while True:
  -        points.append((x0, y0))
  -        if x0 == x1 and y0 == y1:
  -            break
  -        e2 = 2 * err
  -        if e2 > -dy:
  -            err -= dy
  -            x0 += sx
  -        if e2 < dx:
  -            err += dx
  -            y0 += sy
  +    if dx > dy:
  +        err = dx / 2.0
  +        while x != x1:
  +            points.append((x, y))
  +            err -= dy
  +            if err < 0:
  +                y += sy
  +                err += dx
  +            x += sx
  +    else:
  +        err = dy / 2.0
  +        while y != y1:
  +            points.append((x, y))
  +            err -= dx
  +            if err < 0:
  +                x += sx
  +                err += dy
  +            y += sy
  +
  +    points.append((x, y))
       return points
  
  </patch>
golden_diff: diff --git a/Products/CMFPlone/_scripts/verifydb.py b/Products/CMFPlone/_scripts/verifydb.py
  --- a/Products/CMFPlone/_scripts/verifydb.py
  +++ b/Products/CMFPlone/_scripts/verifydb.py
  @@ -64,6 +64,7 @@
       input_file = io.BytesIO(data)
       unpickler = PersistentUnpickler(None, persistent_load, input_file)
       class_info = 'unknown'
  +    pos = None
       try:
           class_info = unpickler.load()
           pos = input_file.tell()
  @@ -77,11 +78,17 @@
           ))
           logger.info(repr(pickle))
           logger.info(traceback.format_exc())
  -        if debug:
  +        if debug and pos is not None:
               try:
                   pickletools.dis(pickle[pos:])
  +            except Exception:
  +                # ignore exceptions while disassembling the pickle since the
  +                # real issue is that it references a unavailable module
  +                pass
               finally:
                   pdb.set_trace()
  +        elif debug and pos is None:
  +            pdb.set_trace()
           return False
       return True
  
verification_info: {"golden_diff": "diff --git a/Products/CMFPlone/_scripts/verifydb.py b/Products/CMFPlone/_scripts/verifydb.py\n--- a/Products/CMFPlone/_scripts/verifydb.py\n+++ b/Products/CMFPlone/_scripts/verifydb.py\n@@ -64,6 +64,7 @@\n     input_file = io.BytesIO(data)\n     unpickler = PersistentUnpickler(None, persistent_load, input_file)\n     class_info = 'unknown'\n+    pos = None\n     try:\n         class_info = unpickler.load()\n         pos = input_file.tell()\n@@ -77,11 +78,17 @@\n         ))\n         logger.info(repr(pickle))\n         logger.info(traceback.format_exc())\n-        if debug:\n+        if debug and pos is not None:\n             try:\n                 pickletools.dis(pickle[pos:])\n+            except Exception:\n+                # ignore exceptions while disassembling the pickle since the\n+                # real issue is that it references a unavailable module\n+                pass\n             finally:\n                 pdb.set_trace()\n+        elif debug and pos is None:\n+            pdb.set_trace()\n         return False\n     return True\n", "issue": "verifydb fails with debug in some cases\nUsing `./bin/instance verifydb -D` to check the `Data.fs` it fails in some cases:\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \"/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py\", line 68, in verify_record\r\n    class_info = unpickler.load()\r\n  File \"/Users/pbauer/.cache/buildout/eggs/ZODB-5.5.1-py3.7.egg/ZODB/_compat.py\", line 62, in find_class\r\n    return super(Unpickler, self).find_class(modulename, name)\r\nModuleNotFoundError: No module named 'Products.Archetypes'\r\n\r\nDuring handling of the above exception, another exception occurred:\r\n\r\nTraceback (most recent call last):\r\n  File \"./bin/instance\", line 262, in <module>\r\n    + sys.argv[1:]))\r\n  File \"/Users/pbauer/.cache/buildout/eggs/plone.recipe.zope2instance-6.1.3-py3.7.egg/plone/recipe/zope2instance/ctl.py\", line 937, in main\r\n    c.onecmd(' '.join(options.args))\r\n  File \"/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/cmd.py\", line 217, in onecmd\r\n    return func(arg)\r\n  File \"/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py\", line 31, in zopectl_entry\r\n    verify_zodb(app, debug=options.debug)\r\n  File \"/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py\", line 50, in verify_zodb\r\n    success = verify_record(oid, data, debug)\r\n  File \"/Users/pbauer/.cache/buildout/eggs/Products.CMFPlone-5.2rc1-py3.7.egg/Products/CMFPlone/_scripts/verifydb.py\", line 82, in verify_record\r\n    pickletools.dis(pickle[pos:])\r\nUnboundLocalError: local variable 'pos' referenced before assignment\r\n```\n", "before_files": [{"content": "# -*- coding: utf-8 -*-\nfrom Zope2.Startup.run import make_wsgi_app\nfrom ZODB.interfaces import IStorageCurrentRecordIteration\nfrom ZODB.serialize import PersistentUnpickler\n\nimport argparse\nimport io\nimport logging\nimport pdb\nimport pickletools\nimport sys\nimport traceback\nimport Zope2\n\nlogger = logging.getLogger('zodbverify')\n\n\ndef zopectl_entry(self, arg):\n    parser = argparse.ArgumentParser(\n        prog=sys.argv[0] + ' verifydb',\n        description='Verifies that all records in the database can be loaded.',\n    )\n    parser.add_argument(\n        '-D', '--debug', action='store_true', dest='debug',\n        help='pause to debug broken pickles')\n    options = parser.parse_args(arg.split(' ') if arg else [])\n\n    logging.basicConfig(level=logging.INFO)\n    make_wsgi_app({}, self.options.configfile)\n    app = Zope2.app()\n    verify_zodb(app, debug=options.debug)\n\n\ndef verify_zodb(obj, debug=False):\n    storage = obj._p_jar._db._storage\n    if not IStorageCurrentRecordIteration.providedBy(storage):\n        raise TypeError(\n            'ZODB storage {} does not implement record_iternext'.format(\n                storage))\n\n    logger.info('Scanning ZODB...')\n\n    next_ = None\n    count = 0\n    errors = 0\n    while True:\n        count += 1\n        oid, tid, data, next_ = storage.record_iternext(next_)\n        logger.debug('Verifying {}'.format(oid))\n        success = verify_record(oid, data, debug)\n        if not success:\n            errors += 1\n        if next_ is None:\n            break\n\n    logger.info(\n        'Done! Scanned {} records. '\n        'Found {} records that could not be loaded.'.format(\n            count, errors)\n    )\n\n\ndef verify_record(oid, data, debug=False):\n    input_file = io.BytesIO(data)\n    unpickler = PersistentUnpickler(None, persistent_load, input_file)\n    class_info = 'unknown'\n    try:\n        class_info = unpickler.load()\n        pos = input_file.tell()\n        unpickler.load()\n    except Exception:\n        input_file.seek(0)\n        pickle = input_file.read()\n        logger.info('\\nCould not process {} record {}:'.format(\n            class_info,\n            repr(oid),\n        ))\n        logger.info(repr(pickle))\n        logger.info(traceback.format_exc())\n        if debug:\n            try:\n                pickletools.dis(pickle[pos:])\n            finally:\n                pdb.set_trace()\n        return False\n    return True\n\n\ndef persistent_load(ref):\n    pass\n", "path": "Products/CMFPlone/_scripts/verifydb.py"}]}