Declaring an object within (vs. outside) a while loop - python-2.7

Question

Given the python 2.7 code below:
# faultReportObj = {}
flatDataObj = []
while row:
faultReportObj = {}
faultReportObj['MessageTime'] = row['MessageTime']
faultReportObj['Event'] = row['Event']
faultReportObj['Subsystem'] = row['Subsystem']
faultReportObj['UnifiedFaultCode'] = row['UnifiedFaultCode']
faultReportObj['FaultDescription'] = row['FaultDescription']
faultReportObj['FaultDetails'] = row['FaultDetails']
faultReportObj['FirstOccurrenceDateTime'] = row['FirstOccurrenceDateTime']
faultReportObj['LastOccurrenceDateTime'] = row['LastOccurrenceDateTime']
faultReportObj['OccurrenceCount'] = row['OccurrenceCount']
print "current row:"
pp.pprint(faultReportObj)
flatDataObj.append(faultReportObj)
row = cursor.fetchone()
conn.close()
pp.pprint(flatDataObj)
If I declare faultReportObj outside the while loop, I get (say) 96 entries in flatDataObj that are all identical to the very last row returned by the query. Note that the pprint statement within the while loop prints the expected (varying) results.
If, as above, I declare faultReportObj inside the loop, flatDataObj is loaded correctly.
Why???? Why is the very last row returned being propagated throughout the entire list?
Thanks!

Answer 1

This is due to list.append inserting a reference to faultReportObj and not copying the value of the dict.
Another way of looking at it:
If you define faultReportObj before the loop, the following occurs:
Create a new dict.
Populate it.
Append a reference to the dict into the list.
Change the dict's content.
Append another reference to the same dict.
etc.
Here's a short piece of code that exemplifies this property:
>>> d = {}
>>> l = []
>>> l.append(d)
>>> d[1] = 2
>>> l
[{1: 2}]
What you want is for step one (Create a new dict) to happen in every iteration of the loop, so that you append a different dict every time.