getattr - Why does Python look for __members__ rather than the requested field? -

i have class defines own __getattr__() in order interact xml tree instantiated objects contain. hides xml structure user , allows him set tag values, etc. if normal fields on object , works fine fields except one: 1 named field. here's how looks:

>>> q = myquery() >>> q.file = "database" >>> print(q) <?xml version="1.0" encoding="utf-8" standalone="yes"?> <requestcollection xmlns="http://dwd.de/sky">   <read>     <select>       <referencedate>         <value></value>       </referencedate>     </select>     <transfer>       <file name="my file"/>     </transfer>   </read> </requestcollection> >>> q.file 

that works fine, side effects should happen so. if try set field field, string method shouldn't returning. clarity, simplified version of __getattr__:

def __getattr__(self, key):     logging.info("looking value key {}.".format(key))     if key == "something"         return self.method_with_side_effect(key)     if key in field_list:         logging.info("key in field list.")         return self.other_method_with_side_effects(key) 

ensemble_member , field both in field_list. check out:

>>> q = myquery() >>> q.ensemble_member looking value key __members__. looking value key __methods__. looking value key ensemble_member. key in field list. ... side effects ... >>> q.field 'station' looking value key __members__. looking value key __methods__. 

the behavior ensemble_member correct, field it's totally incorrect. why that?

i have no methods nor class / object members named field.

another interesting thing is, if put on first line of __getattr__:

def __getattr__(self, key):     if key == "field":         raise valueerror 

the following still happens:

>>> q = myquery() >>> q.field 'station' looking value key __members__. looking value key __methods__. 

what's going on?

i've got - offending code was, in end, these lines:

class skyquery(object):     _unique_fields = ["parameter",                       "ensemble",                       "forecast",                       "station"]     _field_tag_values = [field + "_value" field in _unique_fields] 

naming temporary variable "field" in list comprehension causing problem. python retaining after done. behavior consistent, wasn't expecting it.

i see 3 solutions here (the third suggested user4815162342). implemented third.

1. rename temporary variable x rather field. still have x temporary variable floating around in code, because no members should called x doesn't bother me.

2. call del(field) delete field. don't calling del() , thought clutter code, work if needed able access variable later on.

3. replace list comprehension generator expression list(field + "_value" field in _unique_fields) not share problem