On Sat, Jun 2, 2018 at 2:21 PM, Pål Grønås Drange <paal.dra...@gmail.com> wrote:
> Elevator pitch: > > (2.5h - 14min + 9300ms).total_seconds() > # 8169.3 > > from datetime import datetime as dt > start = dt.now() > end = dt.now() > (end-start) < 5s > # True > > > chrono::duration: > > In C++ 14 the std::chrono::duration was introduced which corresponds > somewhat to > datetime.timedelta. > > C++ 14 introduced so-called chrono literals[1], which are literals > specified as > [number][h|min|s|ms|us|ns], e.g. > > * 2.5h > * 14min > * 9300ms > > These literals should correspond to > > * datetime.timedelta(0, 9000) # 2.5h = 2.5*3600 = 9000 seconds > * datetime.timedelta(0, 840) # 14min = 14*60 = 840 seconds > * datetime.timedelta(0, 9, 300000) # 9300ms = 9 seconds + 3*10^5 > microseconds > > > If a literal was interpreted as a datetime.timedelta, the following would > work > out of the box: > > 2.5h - 14min + 9300ms * 2 > > which would correspond to > > from datetime import timedelta as D > > D(hours=2.5) - D(minutes=14) + D(milliseconds=9300) * 2 > # datetime.timedelta(0, 8178, 600000) # (*2 precedes, so that's to be > expected) > > > (D(hours=2.5) - D(minutes=14) + D(milliseconds=9300)) * 2 > # datetime.timedelta(0, 16338, 600000) > > > > Notes: > > * C++ uses `min` instead of `m`. `min` is a keyword in Python. > * In C++, `1d` means the first day of a month [2]. > * In C++, `1990y` means the year 1990 (in the Proleptic Gregorian > calendar) [3]. > * C++ have the types signed integers and not floats, so 2.5h would not be > valid. > * My apologies if this has been discussed before; my search-fu gave me > nothing. > > > > References: > > > [1] std::literals::chrono_literals::operator""min > http://en.cppreference.com/w/cpp/chrono/operator%22%22min > > [2] http://en.cppreference.com/w/cpp/chrono/day > > [3] http://en.cppreference.com/w/cpp/chrono/year > > > Best regards, > Pål Grønås Drange > IMO datetimes are not common enough to deserve their own literals. It would make the language more complex and harder to learn for a relatively little benefit. This would probably make more sense as a third party lib: >>> import datetimeutils >>> datetimeutils.interpretstr("2.5h - 14min + 9300ms") datetime(...) Both the string and the possibility to specify function arguments would give you way more expressiveness than language literals. -- Giampaolo - http://grodola.blogspot.com
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