strptime format string nasty default

[Jorgen Grahn]

On Wed, 2012-05-09, Javier Novoa C. wrote:
> Hi,
>
> I am using time.strptime method as follows:
>
> I receive an input string, representing some date in the following
> format:
>
> %d%m%Y
>
> However, the day part may be a single digit or two, depending on
> magnitude.
>
> For example:
>
> '10052012' will be parsed as day 10, month 5, year 2012
>
> Again:
>
> '8052012' will be parsed as day 8, month 5, year 2012
>
> What happens when day is 1 or 2?
>
> '1052012' will be parsed as day 10, month 5, year 2012 !!!!
>
> That's not the expected behaviour! Not for me at least. I mean, in my
> case, month will always be a 2 digit string, so there's no ambiguity
> problem by pretending that... say '1052012' is correctly parsed.
>
> Is there a way out of here? I know I can pre-parse the string and
> append a '0' to it when lenght == 7, but I think that a better way
> would be if strptime allowed me to define my format in a better
> way... To say that the month is the optional one-two digit part is
> just a default, isn't it? Why can't I specify that the day part is the
> one with one-or-two digits on the input string...?
>
> Or is there a way out that I don't know yet?

You'd have to read the strptime(3) manual page (it's a Unix function,
imported straight into Python, I'm sure). Judging from a quick read
it's not intended to support things like these. I'm surprised it
doesn't parse your last example to (10, 52, 12) and then fail it due
to month>12.

Can't you use a standard date format, like ISO? Apart from not being
possible to parse with standard functions, this one looks quite odd
and isn't very human-readable.

If you have to use this format, I strongly recommend parsing it
"manually" as text first. Then you can create an ISO date and feed
that to strptime, or perhaps use your parsed (day, month, year) tuple
directly.

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .     .
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