Implement __format__ on cfdm.Data objects

[davidhassell]

When including cfdm.Data objects in f-strings that include format codes (such as .3f), size 1 arrays should be formatted like their python scalar counterparts.

I think that the desired behaviour would be:

>>> d = cfdm.Data(9, 'metres')
>>> f"{d}"
'9 metres'
>>> f"{d!s}"
'9 metres'
>>> f"{d!r}"
'<Data(): 9 metres>'
>>> f"{d:.3f}"
'9.000'

>>> d = cfdm.Data([[9]], 'metres')
>>> f"{d}"
'[[9]] metres'
>>> f"{d!s}"
'[[9]] metres'
>>> f"{d!r}"
'<Data(1, 1): [[9]] metres>'
>>> f"{d:.3f}"
'9.000'

>>> d = cfdm.Data([9, 10], 'metres')
>>> f"{d}"
>>> '[9, 10] metres'
>>> f"{d!s}"
>>> '[9, 10] metres'
>>> f"{d!r}"
'<Data(2): [9, 10] metres>'
>>> f"{d:.3f}"
    ...
ValueError: Can't format Data array of size 2 with format code .3f

@JonathanGregory, does this look like what you would expect?

[JonathanGregory]

Yes, thank you, that looks perfect. Jonathan

[davidhassell]

Thanks - PR to follow ...