[Python-Dev] bpo-36558: Change time.mktime() return type from float to int?

Ivan Pozdeev vano at mail.mipt.ru
Tue Apr 16 11:47:35 EDT 2019

On 16.04.2019 17:24, Victor Stinner wrote:
> Hi,
> time.mktime() looks "inconsistent" to me and I would like to change
> it, but I'm not sure how it impacts backward compatibility.
> https://bugs.python.org/issue36558
> time.mktime() returns a floating point number:
>>>> type(time.mktime(time.localtime()))
> <class 'float'>
> The documentation says:
> "It returns a floating point number, for compatibility with :func:`.time`."
> time.time() returns a float because it has sub-second resolution, but
> the C function mktime() returns an integer number of seconds.
> Would it make sense to change mktime() return type from float to int?
> I would like to change mktime() return type to make the function more
> consistent: all inputs are integers, it sounds wrong to me to return
> float. The result should be integer as well.
> How much code would it break? I guess that the main impact are unit
> tests relying on repr(time.mktime(t)) exact value. But it's easy to
> fix the tests: use int(time.mktime(t)) or "%.0f" % time.mktime(t) to
> never get ".0", or use float(time.mktime(t))) to explicitly cast for a
> float (that which be a bad but quick fix).
I envision it breaking code that relies on implicitly inferring the type of the result from the types of both operands (e.g. arithmetic 
But for mktime() specifically, I presume the amount of such code very small.
> Note: I wrote and implemented the PEP 564 to avoid any precision loss.
> mktime() will not start loosing precision before year 285,422,891
> (which is quite far in the future ;-)).
> Victor


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