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Comment by libeclipse | Hacker News Reader

I tend to use the old style ("%s" % "lel"). Just wondering, does this affect that too?

Attribute access doesn't seem to work with old-style formatting, so I would think it's safe.

    >>> class foo:
    ...     def __init__(self, **kwargs):
    ...             self.__dict__.update(kwargs)
    ...
    >>> my_foo = foo(secret="bazinga")
    >>>
    >>> "%(foo)s" % {'foo': my_foo}
    '<__main__.foo instance at 0x1101d23f8>'
    >>>
    >>> "%(foo.secret)s" % {'foo': my_foo}
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    KeyError: 'foo.secret'

The nice thing about the new format is that you can reverse the order of the variables inside the string, which is nice when you're localizing strings into languages with a reversed sentence structures, like Japanese. I haven't done a ton of Python, but the old style won't let you do that, will it?

Reversing the order is not possible, but you can use a dict instead:

    >>> "%(foo)s" % {"foo": "bar"}
    'bar'

Heyyyyyy I did not know that. TIL, thank you.

Funny. I thought Python implemented all the quirks of the original printf() formatting, including using arguments at specific positions. Apparently it didn't (and arguably it's a good thing).

  $ printf '%2$s %2$s %1$s\n' aaa bbb
  bbb bbb aaa

Yes, it will, just use named placeholders: "%(some)s" % {'some': 'helllo'}

I'm not sure I understand the use case for reversing the formatting variables, but you could do this to make old-style formatting work that way:

    >>> 'hello, %s %s' % tuple(reversed(['smith', 'bob']))
    'hello, bob smith'

I think it's more readable if you abstract that bit into a lambda function:

    >>> rev_args = lambda *args: tuple(reversed(args))
    >>> 'hello, %s %s' % rev_args('smith', 'bob')
    'hello, bob smith'

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