Deviations and Extensions to the OData Spec

There are some minor cases where this library deviates from the official spec, e.g. when the spec is ambiguous, or to add extra non-breaking functionality.

Lists with a single item need a trailing comma

This library needs a trailing comma to represent a list with a single item, whereas the spec does not describe this trailing comma (e.g. (item,) instead of (item)).

The reason is that the spec doesn’t seem to differentiate between a list of a single item and any other parenthesized expression. This can lead to parsing conflicts. Consider the following expression:

concat(('a'), ('b'))

The grammar in the official spec could parse this as either:

Concatenate 2 lists, the first one containing the single string ‘a’, the second one containing the single string ‘b’. The result would be ('a', 'b').
Concatenate 2 expressions in parentheses. The first one is the string literal ‘a’, the second one the string literal ‘b’. The result would be 'ab'

To make this difference explicit, this library requires a trailing comma to signify a list. The same behavior is present in Python:

>>> ("a")
'a'
>>> ("a",)
('a',)

>>> parser.parse(lexer.tokenize("('a')"))
String(val='a')
>>> parser.parse(lexer.tokenize("('a',)"))
List(val=[String(val='a')])

Durations expressed in years and months

The official spec defines a duration with a number of days, hours, minutes, and seconds. E.g. duration'P1DT2H' is a duration of 1 Day and 2 Hours.

This library adds the ability to express durations containing Years and Months. E.g. duration'P1Y2M3DT4H' would express a duration of 1 Year, 2 Months, 3 Days, and 4 Hours.

It’s important to note that the final internal value is still expressed in days, based on average durations. Thus, a month simply represents 30.44 days, while a year represents 365.25 days.