CODEWITHSUNDEEP
pythonlistclassvariables
Malgi
Malgi

Reputation: 730

How to get list of class variables in the order they are defined?

I have a class that specifies the column layout of a csv file as:

class RecordLayout(object):
    YEAR = 0
    DATE = 1
    MONTH = 2
    ID = 3
    AGE = 4
    SALARY = 5

I need to get the list of the class variables in the order they are defined.

So far, I tried:

[attr for attr in dir(RecordLayout()) if not callable(attr) and not attr.startswith("__")]

but it returns:

['AGE', 'DATE', 'ID', 'MONTH', 'SALARY', 'YEAR']

which is the class variables ordered alphabetically. I need the variables to be returned in the order they are defined in the class:

['YEAR', 'DATE', 'MONTH', 'ID', 'AGE', 'SALARY']

Is there a way to achieve this?

Upvotes: 1

Views: 270

Answers (2)

greg
greg

Reputation: 562

Old question but top google search result, so here's my answer after some more research.

Use RecordLayout().__dir__() and filter out the entries which are not needed. __dir__() should provide the entries in the order they were defined, whereas dir() applies a sort.

How did I get here?

Starting with "PEP 520 -- Preserving Class Attribute Definition Order" and then ended up at this discussion thread https://mail.python.org/pipermail/python-dev/2016-September/146382.html

  >>> class Example:
  ...     def __dir__(self):
  ...         return "first second third fourth".split()
  ...
  >>> dir(Example())
  ['first', 'fourth', 'second', 'third']
  >>> Example().__dir__()
  ['first', 'second', 'third', 'fourth']

Upvotes: 0

Daniel Roseman
Daniel Roseman

Reputation: 599580

You should use an Enum for this.

>>> class RecordLayout(Enum):
...     YEAR = 0
...     DATE = 1
...     MONTH = 2
...     ID = 3
...     AGE = 4
...     SALARY = 5
...
>>> for i in RecordLayout:
...   print(i)
...
RecordLayout.YEAR
RecordLayout.DATE
RecordLayout.MONTH
RecordLayout.ID
RecordLayout.AGE
RecordLayout.SALARY

Upvotes: 3

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