[Python-ideas] datetime.timedelta literals

[Pål Grønås Drange]

For the general user-defined literals, here are some example use cases:

Here is how to expose literals:

__literals__ = ['__literal_h__', '__literal_min__', '__literal_s__']

And here is how to import them:

from mymodule import _*  # imports all literals from mymodule
# could also be *_ or ** or ~ or __literals__ ?

90_deg  # 1.0 in rad
20_°C   # 293.15 Kelvin

units.to(20.0_mi, 'km')

e = 1_X + 4_G + 13_M + 180_k  # SI scale factors can easily be implemented

p = 3_x - 2_y + 1_z  # Coordinate in 3D

M = 4_I  # The 4x4 Identity Matrix

p * 2_pi  # because it's simpler than 2 * np.pi
p * 11_π   # why not

d = 2_sqrt  # sqrt(2), or simply 2**(1/2), not a killer argument

h1 = 30_px
h2 = 4_em  # sizes for typography
c = 'ffff00'_color  # the color yellow
h = 'My header'_h3  # renders <h3>My header</h3> or something

g = 9.81_m_div_ss  # that was ugly ...

'More weird examples'_info  # log.info(msg)

'2018-06-04'_AD  # is a date

'192.168.0.42'_ip4  # why not?

'USER'_os  # = os.environ.get(x, '')

# Can have state?
initialize(80)  # set default string width to 80 chars
'my string'_c  # will now be centralized in 80 chars
'my string'_l  # will now be left aligned in 80 chars
'my string'_r  # will now be right aligned in 80 chars


If we used, e.g. tilde, we could even use it on function calls

y = fun(x)~dx  # differentiations!  Like decorators, but on "call time"

I accept that introducing a new symbol has a very high threshold, and
will not go through.  I just wanted to mention it.


Yes, we could write all these as easily as function calls,

deg(90)
celsius(20)
center('my string')  # or 'my string'.center(80)

But somehow it seems nicer to write 42_km than 12 * pint.UnitRegistry().km


- Pål
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