按字母顺序输出对象的属性和值

Question

I need to generate an export (csv) of a series of simple objects like this:

class trx:
   def __init__(self,
                 file_name='',
                 bank='',
                 trans_type='',
                 account=''):

        self.filename = file_name
        self.bank = bank
        self.trans_type = trans_type
        self.account = account

What is the simplest way to list the attribute/value pairs in order by attribute? __dict__ changes order every time.

Answer 1

You could use vars() on self , then sort the items:

sorted(vars(self).items())

This then gives you a sorted list of (attributename, value) pairs.

However, if your class is little more than a container for 4 related datapoints, then consider using a namedtuple class :

from collections import namedtuple

TRX = namedtuple('TRX', ('file_name', 'bank', 'trans_type', 'account'))

This lists the attributes in named order, always:

>>> from collections import namedtuple
>>> TRX = namedtuple('TRX', ('file_name', 'bank', 'trans_type', 'account'))
>>> TRX('foo.txt', 'Bar PLC', 'withdrawal', '1234xyz')
TRX(file_name='foo.txt', bank='Bar PLC', trans_type='withdrawal', account='1234xyz')

Because the instances are sequences (a subclass of tuple in fact) you can pass these directly to a csv.writer().writerow() call ; at the same time you can use instance.bank or instance.file_name to access the fields.

Another alternative is to use dictionaries , and use csv.DictWriter() to handle the order (the fieldnames argument determines the order).