Refactor long try-except chain

问题

I have a feeling that this sequence might be written shorter:

dim = Dimension.objects.get(pk=rows['pk'])
try:
    dim.name = rows['name']
except KeyError:
    pass
try:
    dim.external_flg = rows['external_flg']
except:
    pass
try:
    dim.ext_owner = rows['ext_owner']
except KeyError:
    pass
try:
    dim.ext_table_name = rows['ext_table_name']
except KeyError:
    pass
try:
    dim.ext_start_date_column_name = rows['ext_start_date_column_name']
except KeyError:
    pass
try:
    dim.ext_end_date_column_name = rows['ext_end_date_column_name']
except KeyError:
    pass

I've never had any experience in Python code optimization and working with exceptions but I'd be glad to have an alternative examples how it could be shortened.

Thank you!

回答1:

Use the dict.get() method:

dim.name = rows.get('name', dim.name)

Or, for more DRY solution, put all assignments into the loop:

for field_name in ('name', 'external_flg', 'ext_owner', 'ext_table_name',
                   'ext_start_date_column_name', 'ext_end_date_column_name'):
    if field_name in rows:
        setattr(dim, field_name, rows[field_name])

To handle the list data you can make the similar loop:

for i, field_name in enumerate(('name', 'external_flg', 'ext_owner',
                                'ext_table_name', 'ext_start_date_column_name',
                                'ext_end_date_column_name')):
    if i < len[rows]:
        setattr(dim, field_name, rows[i])

回答2:

Something like this should work — this answer includes try/catch block to catch KeyError :-)

attributes = ['name', 'external_flg', 'ext_owner', 'ext_table_name',
               'ext_start_date_column_name', 'ext_end_date_column_name']

dim = Dimension.objects.get(pk=rows['pk'])

for attr in attributes:
    try:
        setattr(dim, attr, rows[attr])
    except KeyError:
        pass

来源：https://stackoverflow.com/questions/28876799/refactor-long-try-except-chain