pluck: Quickly pluck "fields" from a list of values

pluck is the simplest way of plucking "fields" from an iterable of values. "Fields" are either item.field or item[field]. Pluck tries both, in that order. If nothing is found, and no default value is specified, it throws an exception.

Usage

The package consists of one module consisting of two functions:

from pluck import pluck, ipluck

ipluck is just the iterable version of pluck. Use it like this:

pluck(iterable, key)

or:

pluck(iterable, *keys)

Examples

A simple example first. Say you have a list of datetimes:

>>> from pluck import pluck
>>> dates = [
...     datetime(2012, 10, 22, 12, 00),
...     datetime(2012, 10, 22, 15, 14),
...     datetime(2012, 10, 22, 21, 44),
... ]
>>> pluck(dates, 'day')
[22, 22, 22]
>>> pluck(dates, 'hour')
[12, 15, 21]

It also works on dictionary-like access (__getitem__):

>>> objects = [
...      {'id': 282, 'name': 'Alice', 'age': 30, 'sex': 'female'},
...      {'id': 217, 'name': 'Bob', 'age': 56},
...      {'id': 328, 'name': 'Charlie', 'age': 56, 'sex': 'male'},
... ]
>>> pluck(objects, 'name')
['Alice', 'Bob', 'Charlie']
>>> pluck(objects, 'age')
[30, 56, 56]

You can also combine these into a single pluck:

>>> pluck(objects, 'name', 'age')
[('Alice', 30), ('Bob', 56), ('Charlie', 56)]

Defaults

You can specify default values, too. By default, pluck will throw an exception when a "field" does not exist:

>>> pluck(objects, 'sex')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pluck.py", line 104, in pluck
      return list(ipluck(iterable, *keys, **kwargs))
  File "pluck.py", line 49, in getter
      raise ValueError('Item %r has no attr or key for %r' % (item, key))
  ValueError: Item {'age': 56, 'id': 217, 'name': 'Bob'} has no attr or key for 'sex'

To instead fill these places with a default value, use this:

>>> pluck(objects, 'sex', default='unknown')
['female', 'unknown', 'male']

When you specify multiple keys, you need to use the defaults (plural!) keyword argument instead:

>>> pluck(objects, 'name', 'sex', defaults={'sex': 'unknown'})
[('Alice', 'female'), ('Bob', 'unknown'), ('Charlie', 'male')]

Iterator, rather?

Use ipluck if you'd rather wanna have an iterator:

>>> from pluck import ipluck
>>> ipluck(large_stream_of_items, 'name')
<itertools.imap object at 0x10c7515d0>

pluck is equivalent to list(ipluck(...)).