sseg/kwlist

Keyword lists in Python

KeywordList

kwlist provides a KeywordList class for associating string keywords with multiple values in a consistent order.

This is useful for specifying multiple values for arguments as in HTTP headers or query parameters.

Inspired by Elixir's Keyword module.

Examples

Basic usage:

>>> from kwlist import KeywordList

>>> a = KeywordList(foo=1, bar=2)
>>> b = KeywordList(foo=3, baz=4)
>>> c = a + b
>>> c
KeywordList[foo: 1, bar: 2, foo: 3, baz: 4]
>>> a == [("foo", 1), ("bar", 2)]
True
>>> "bar" in b
False
>>> c["foo"]
1
>>> list(c.get_all("foo"))
[1, 3]

A KeywordList can be built by passing tuples of keyword-value pairs or keyword arguments or both:

>>> a = KeywordList(("foo", 1), ("bar", 2))
>>> b = KeywordList(foo=3, baz=4)
>>> a + b == KeywordList(("foo", 1), ("foo", 3), bar=2, baz=4)
True

Note that keyword argument ordering is only preserved in Python 3.6+ (see PEP 468).

All methods of the KeywordList return new objects without mutating the object invoked:

>>> original = KeywordList(a=2)
>>> original.update('a', lambda n: n + 1)
KeywordList[a: 3]
>>> original.delete('a')
KeywordList[]
>>> original.put('a', None)
KeywordList[a: None]
>>> original
KeywordList[a: 2]

This property simplifies arbitrary and complex operator chaining:

>>> original = KeywordList()
>>> original.append([("foo", 1), ("foo", 2), ("bar", 3)]).transform(lambda x: str(x ** 2)).split("foo")
KeywordList[foo: '1', foo: '4'], KeywordList[bar: '9']

Installing

Ideally in a virtual environment, run:

git clone https://github.com/sseg/kwlist.git && pip install kwlist/

Similar Projects

If you're looking for something closer to Python's dict API you might like one of these implementations:

• Werkzeug multidict
• stdlib Headers object
• aiohttp multidict
• ordered multidict

License

BSD licensed. See the LICENSE file for details.