iterating over DictRow

Dear all,

I cannot currently wrap my head around why I am seeing this:

2020-09-23 23:30:23 gmConnectionPool.py::<module>() #87): psycopg2 module version: 2.8.5 (dt dec pq3 ext)
2020-09-23 23:30:23 gmConnectionPool.py::<module>() #88): PostgreSQL via DB-API module "<module 'psycopg2' from '/usr/lib/python3/dist-packages/psycopg2/__init__.py'>": API level 2.0, thread safety 2, parameter style "pyformat"
2020-09-23 23:30:23 gmConnectionPool.py::<module>() #89): libpq version (compiled in): 120002
2020-09-23 23:30:23 gmConnectionPool.py::<module>() #90): libpq version (loaded now) : 120004
...
2020-09-23 23:30:28 gmConnectionPool.py::__log_on_first_contact() #445): heed Prime Directive
2020-09-23 23:30:28 gmConnectionPool.py::__log_on_first_contact() #457): PostgreSQL version (numeric): 11.7
...
2020-09-23 23:31:02 gmMacro.py::_get_variant_diagnoses() #2442): [[260, 'L: Bewegungsapparat', False, 'B', 'clin.health_issue'], [260, 'K: aHT/HI', False, 'B', 'clin.health_issue'], [260, 'D: Verdauung', False, None, 'clin.health_issue']]
2020-09-23 23:31:02 gmMacro.py::_get_variant_diagnoses() #2443): <class 'psycopg2.extras.DictRow'>
2020-09-23 23:31:02 gmMacro.py::_escape_dict() #2851): 260
2020-09-23 23:31:02 gmMacro.py::__getitem__() #880): placeholder handling error: diagnoses:: \item %(diagnosis)s::
Traceback (most recent call last):
File "/home/ncq/Projekte/gm/git/gnumed/gnumed/Gnumed/wxpython/gmMacro.py", line 869, in __getitem__
val = handler(data = options)
File "/home/ncq/Projekte/gm/git/gnumed/gnumed/Gnumed/wxpython/gmMacro.py", line 2445, in _get_variant_diagnoses
return '\n'.join(template % self._escape_dict(dx, none_string = '?', bool_strings = [_('yes'), _('no')]) for dx in selected)
File "/home/ncq/Projekte/gm/git/gnumed/gnumed/Gnumed/wxpython/gmMacro.py", line 2445, in <genexpr>
return '\n'.join(template % self._escape_dict(dx, none_string = '?', bool_strings = [_('yes'), _('no')]) for dx in selected)
File "/home/ncq/Projekte/gm/git/gnumed/gnumed/Gnumed/wxpython/gmMacro.py", line 2852, in _escape_dict
val = the_dict[field]
File "/usr/lib/python3/dist-packages/psycopg2/extras.py", line 169, in __getitem__
return super(DictRow, self).__getitem__(x)
IndexError: list index out of range

This line logs a list of DictRow's:

2020-09-23 23:31:02 gmMacro.py::_get_variant_diagnoses() #2442): [[260, 'L: Bewegungsapparat', False, 'B', 'clin.health_issue'], [260, 'K: aHT/HI', False, 'B', 'clin.health_issue'], [260, 'D: Verdauung', False, None, 'clin.health_issue']]

as evidenced here:

2020-09-23 23:31:02 gmMacro.py::_get_variant_diagnoses() #2443): <class 'psycopg2.extras.DictRow'>

The logging code:

_log.debug('%s', selected)
_log.debug('%s', type(selected[0]))

and then iterates over the list of DictRow's as per list
comprehension like so:

return '\n'.join(template % self._escape_dict(dx, none_string = '?', bool_strings = [_('yes'), _('no')]) for dx in selected)

where _escape_dict() does this:

def _escape_dict(self, the_dict=None, date_format='%Y %b %d %H:%M', none_string='', bool_strings=None):
data = {}
for field in the_dict:
_log.debug('%s', field)
val = the_dict[field]
if val is None:
...
if isinstance(val, bool):
...
if isinstance(val, datetime.datetime):
...
if self.__esc_style in ['latex', 'tex']:
...
elif self.__esc_style in ['xetex', 'xelatex']:
...
return data

Iterating over the_dict should work for lists (produces
values) OR dicts (produces keys, under py3). It seems as if
the line

for field in the_dict: # I hoped to iterate over the keys = column names

somehow "decides": "currently we are treating the_dict as a
list (after all, it is a DictRow, which _can_ be treated as a
list) which then "turns" the dict-style access in

val = the_dict[field]

into a list access.

Somehow I have a feeling that due to the type of "field"
-- it being integer (namely, a primary key) -- forces

the_dict[field]

to attempt a list-style index based access (which fails, due
to there not being 260 columns in the SQL query result :-)

Solutions that come to mind:

_Must_ I use RealDictCursor() to safely avoid this trap ?

(or else dict()ify DictRow's as needed)

Any insights to be had ?

Thanks,
Karsten
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