Package: backpack
Backpack########.. image:: https://travis-ci.org/sdispater/backpack.png:alt: Backpack Build status:target: https://travis-ci.org/sdispater/backpackUseful utilities for Python.Supports Python **2.7+** and **3.2+**.Collection==========The ``Collection`` class provides a fluent, convenient wrapper for working with list  of data.To instantiatte a ``Collection`` you can also use the ``collection()`` helper.Available Methods*****************For the remainder of this documentation, we'll discuss each method available on the ``Collection`` class.Remember, all of these methods may be chained for fluently manipulating the underlying list or dict.Furthermore, almost every method returns a new ``Collection`` instance,allowing you to preserve the original copy of the collection when necessary.You may select any method from this table to see an example of its usage:* all_* avg_* chunk_* collapse_* contains_* count_* diff_* each_* every_* filter_* first_* flatten_* forget_* for_page_* get_* implode_* is_empty_* last_* map_* merge_* pluck_* pop_* prepend_* pull_* push_* put_* reduce_* reject_* reverse_* serialize_* shift_* sort_* sum_* take_* to_json_* transform_* unique_* where_* zip_Methods Listing***************.. _all:``all()``---------The ``all`` method simply returns the underlying list represented by the collection:.. code-block:: pythonCollection([1, 2, 3]).all()# [1, 2, 3].. _avg:``avg()``---------The ``avg`` method returns the average of all items in the collection:.. code-block:: pythonCollection([1, 2, 3, 4, 5]).avg()# 3If the collection contains nested objects or dictionaries, you must pass a key to use for determiningwhich values to calculate the average:.. code-block:: pythoncollection = Collection([{'name': 'JavaScript: The Good Parts', 'pages': 176},{'name': 'JavaScript: The Defnitive Guide', 'pages': 1096}])collection.avg('pages')# 636.. _chunk:``chunk()``-----------The ``chunk`` method breaks the collection into multiple, smaller collections of a given size:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5, 6, 7])chunks = collection.chunk(4)chunks.serialize()# [[1, 2, 3, 4], [5, 6, 7]].. _collapse:``collapse()``--------------The ``collapse`` method collapses a collection of lists into a flat collection:.. code-block:: pythoncollection = Collection([[1, 2, 3], [4, 5, 6], [7, 8, 9]])collapsed = collection.collapse()collapsed.all()# [1, 2, 3, 4, 5, 6, 7, 8, 9].. _contains:``contains()``--------------The ``contains`` method determines whether the collection contains a given item:.. code-block:: pythoncollection = Collection(['foo', 'bar'])collection.contains('foo')# TrueYou can also use the ``in`` keyword:.. code-block:: python'foo' in collection# TrueYou can also pass a key / value pair to the ``contains`` method,which will determine if the given pair exists in the collection:.. code-block:: pythoncollection = Collection([{'name': 'John', 'id': 1},{'name': 'Jane', 'id': 2}])collection.contains('name', 'Simon')# FalseFinally, you may also pass a callback to the ``contains`` method to perform your own truth test:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5])collection.contains(lambda item: item > 5)# False.. _count:``count()``-----------The ``count`` method returns the total number of items in the collection:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])collection.count()# 4The ``len`` function can also be used:.. code-block:: pythonlen(collection)# 4.. _diff:``diff()``----------The ``diff`` method compares the collection against another collection, a ``list`` or a ``dict``:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5])diff = collection.diff([2, 4, 6, 8])diff.all()# [1, 3, 5].. _each:``each()``----------The ``each`` method iterates over the items in the collection and passes each item to a given callback:.. code-block:: pythonposts.each(lambda post: post.author().save(author))Return ``False`` from your callback to break out of the loop:.. code-block:: pythonposts.each(lambda post: post.author().save(author) if author.name == 'John' else False).. _every:``every()``-----------The ``every`` method creates a new collection consisting of every n-th element:.. code-block:: pythoncollection = Collection(['a', 'b', 'c', 'd', 'e', 'f'])collection.every(4).all()# ['a', 'e']You can optionally pass the offset as the second argument:.. code-block:: pythoncollection.every(4, 1).all()# ['b', 'f'].. _filter:``filter()``------------The ``filter`` method filters the collection by a given callback,keeping only those items that pass a given truth test:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])filtered = collection.filter(lambda item: item > 2)filtered.all()# [3, 4].. _first:``first()``-----------The ``first`` method returns the first element in the collectionthat passes a given truth test:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])collection.first(lambda item: item > 2)# 3You can also call the ``first`` method with no argumentsto get the first element in the collection.If the collection is empty, ``None`` is returned:.. code-block:: pythoncollection.first()# 1.. _flatten:``flatten()``-------------The ``flatten`` method flattens a multi-dimensional collection into a single dimension:.. code-block:: pythoncollection = Collection([1, 2, [3, 4, 5, {'foo': 'bar'}]])flattened = collection.flatten()flattened.all()# [1, 2, 3, 4, 5, 'bar'].. _forget:``forget()``------------The ``forget`` method removes an item from the collection by its key:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5])collection.forget(1)collection.all()# [1, 3, 4, 5].. warning::Unlike most other collection methods, ``forget`` does not return a new modified collection;it modifies the collection it is called on... _for_page:``for_page()``--------------The ``for_page`` method returns a new collection containingthe items that would be present on a given page number:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5, 6, 7, 8, 9])chunk = collection.for_page(2, 3)chunk.all()# 4, 5, 6The method requires the page number and the number of items to show per page, respectively... _get:``get()``---------The ``get`` method returns the item at a given key. If the key does not exist, ``None`` is returned:.. code-block:: pythoncollection = Collection([1, 2, 3])collection.get(3)# NoneYou can optionally pass a default value as the second argument:.. code-block:: pythoncollection = Collection([1, 2, 3])collection.get(3, 'default-value')# default-value.. _implode:``implode()``-------------The ``implode`` method joins the items in a collection.Its arguments depend on the type of items in the collection.If the collection contains dictionaries or objects,you must pass the key of the attributes you wish to join,and the "glue" string you wish to place between the values:.. code-block:: pythoncollection = Collection([{'account_id': 1, 'product': 'Desk'},{'account_id': 2, 'product': 'Chair'}])collection.implode('product', ', ')# Desk, ChairIf the collection contains simple strings,simply pass the "glue" as the only argument to the method:.. code-block:: pythoncollection = Collection(['foo', 'bar', 'baz'])collection.implode('-')# foo-bar-baz.. _is_empty:``is_empty()``--------------The ``is_empty`` method returns ``True`` if the collection is empty; otherwise, ``False`` is returned:.. code-block:: pythonCollection([]).is_empty()# True.. _last:``last()``----------The ``last`` method returns the last element in the collection that passes a given truth test:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])last = collection.last(lambda item: item < 3)# 2You can also call the ``last`` method with no arguments to get the last element in the collection.If the collection is empty, ``None`` is returned:.. code-block:: pythoncollection.last()# 4.. _map:``map()``---------The ``map`` method iterates through the collection and passes each value to the given callback.The callback is free to modify the item and return it, thus forming a new collection of modified items:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])multiplied = collection.map(lambda item: item * 2)multiplied.all()# [2, 4, 6, 8].. warning::Like most other collection methods, ``map`` returns a new ``Collection`` instance;it does not modify the collection it is called on.If you want to transform the original collection, use the transform_ method... _merge:``merge()``-----------The merge method merges the given list into the collection:.. code-block:: pythoncollection = Collection(['Desk', 'Chair'])collection.merge(['Bookcase', 'Door'])collection.all()# ['Desk', 'Chair', 'Bookcase', 'Door'].. warning::Unlike most other collection methods, ``merge`` does not return a new modified collection;it modifies the collection it is called on... _pluck:``pluck()``-----------The ``pluck`` method retrieves all of the collection values for a given key:.. code-block:: pythoncollection = Collection([{'product_id': 1, 'product': 'Desk'},{'product_id': 2, 'product': 'Chair'}])plucked = collection.pluck('product')plucked.all()# ['Desk', 'Chair']You can also specify how you wish the resulting collection to be keyed:.. code-block:: pythonplucked = collection.pluck('name', 'product_id')plucked# {1: 'Desk', 2: 'Chair'}.. _pop:``pop()``---------The ``pop`` method removes and returns the last item from the collection:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5])collection.pop()# 5collection.all()# [1, 2, 3, 4].. _prepend:``prepend()``-------------The ``prepend`` method adds an item to the beginning of the collection:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])collection.prepend(0)collection.all()# [0, 1, 2, 3, 4].. _pull:``pull()``----------The ``pull`` method removes and returns an item from the collection by its key:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])collection.pull(1)collection.all()# [1, 3, 4].. _push:``push()``/``append()``-----------------------The ``push`` (or ``append``) method appends an item to the end of the collection:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])collection.push(5)collection.all()# [1, 2, 3, 4, 5].. _put:``put()``---------The ``put`` method sets the given key and value in the collection:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])collection.put(1, 5)collection.all()# [1, 5, 3, 4].. note::It is equivalent to:.. code-block:: pythoncollection[1] = 5.. _reduce:``reduce()``------------The ``reduce`` method reduces the collection to a single value,passing the result of each iteration into the subsequent iteration:.. code-block:: pythoncollection = Collection([1, 2, 3])collection.reduce(lambda result, item: (result or 0) + item)# 6The value for ``result`` on the first iteration is ``None``;however, you can specify its initial value by passing a second argument to reduce:.. code-block:: pythoncollection.reduce(lambda result, item: result + item, 4)# 10.. _reject:``reject()``------------The ``reject`` method filters the collection using the given callback.The callback should return ``True`` for any items it wishes to remove from the resulting collection:.. code-block:: pythoncollection = Collection([1, 2, 3, 4])filtered = collection.reject(lambda item: item > 2)filtered.all()# [1, 2]For the inverse of ``reject``, see the filter_ method... _reverse:``reverse()``-------------The ``reverse`` method reverses the order of the collection's items:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5])reverse = collection.reverse()reverse.all()# [5, 4, 3, 2, 1].. _serialize:``serialize()``---------------The ``serialize`` method converts the collection into a ``list``.If the collection's values are :ref:`ORM` models, the models will also be converted to dictionaries:.. code-block:: pythoncollection = Collection([User.find(1)])collection.serialize()# [{'id': 1, 'name': 'John'}].. warning::``serialize`` also converts all of its nested objects.If you want to get the underlying items as is, use the all_ method instead... _shift:``shift()``-----------The ``shift`` method removes and returns the first item from the collection:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5])collection.shift()# 1collection.all()# [2, 3, 4, 5].. _sort:``sort()``----------The ``sort`` method sorts the collection:.. code-block:: pythoncollection = Collection([5, 3, 1, 2, 4])sorted = collection.sort()sorted.all()# [1, 2, 3, 4, 5].. _sum:``sum()``---------The ``sum`` method returns the sum of all items in the collection:.. code-block:: pythonCollection([1, 2, 3, 4, 5]).sum()# 15If the collection contains dictionaries or objects, you must pass a key to use for determining which values to sum:.. code-block:: pythoncollection = Collection([{'name': 'JavaScript: The Good Parts', 'pages': 176},{'name': 'JavaScript: The Defnitive Guide', 'pages': 1096}])collection.sum('pages')# 1272In addition, you can pass your own callback to determine which values of the collection to sum:.. code-block:: pythoncollection = Collection([{'name': 'Chair', 'colors': ['Black']},{'name': 'Desk', 'colors': ['Black', 'Mahogany']},{'name': 'Bookcase', 'colors': ['Red', 'Beige', 'Brown']}])collection.sum(lambda product: len(product['colors']))# 6.. _take:``take()``----------The ``take`` method returns a new collection with the specified number of items:.. code-block:: pythoncollection = Collection([0, 1, 2, 3, 4, 5])chunk = collection.take(3)chunk.all()# [0, 1, 2]You can also pass a negative integer to take the specified amount of items from the end of the collection:.. code-block:: pythonchunk = collection.chunk(-2)chunk.all()# [4, 5].. _to_json:``to_json()``-------------The ``to_json`` method converts the collection into JSON:.. code-block:: pythoncollection = Collection([{'name': 'Desk', 'price': 200}])collection.to_json()# '[{"name": "Desk", "price": 200}]'.. _transform:``transform()``---------------The ``transform`` method iterates over the collection and calls the given callbackwith each item in the collection.The items in the collection will be replaced by the values returned by the callback:.. code-block:: pythoncollection = Collection([1, 2, 3, 4, 5])collection.transform(lambda item: item * 2)collection.all()# [2, 4, 6, 8, 10].. warning::Unlike most other collection methods, ``transform`` modifies the collection itself.If you wish to create a new collection instead, use the map_ method... _unique:``unique()``------------The ``unique`` method returns all of the unique items in the collection:.. code-block:: pythoncollection = Collection([1, 1, 2, 2, 3, 4, 2])unique = collection.unique()unique.all()# [1, 2, 3, 4]When dealing with dictionaries or objects, you can specify the key used to determine uniqueness:.. code-block:: pythoncollection = Collection([{'name': 'iPhone 6', 'brand': 'Apple', 'type': 'phone'},{'name': 'iPhone 5', 'brand': 'Apple', 'type': 'phone'},{'name': 'Apple Watch', 'brand': 'Apple', 'type': 'watch'},{'name': 'Galaxy S6', 'brand': 'Samsung', 'type': 'phone'},{'name': 'Galaxy Gear', 'brand': 'Samsung', 'type': 'watch'}])unique = collection.unique('brand')unique.all()# [#     {'name': 'iPhone 6', 'brand': 'Apple', 'type': 'phone'},#     {'name': 'Galaxy S6', 'brand': 'Samsung', 'type': 'phone'}# ]You can also pass your own callback to determine item uniqueness:.. code-block:: pythonunique = collection.unique(lambda item: item['brand'] + item['type'])unique.all()# [#     {'name': 'iPhone 6', 'brand': 'Apple', 'type': 'phone'},#     {'name': 'Apple Watch', 'brand': 'Apple', 'type': 'watch'},#     {'name': 'Galaxy S6', 'brand': 'Samsung', 'type': 'phone'},#     {'name': 'Galaxy Gear', 'brand': 'Samsung', 'type': 'watch'}# ].. _where:``where()``-----------The ``where`` method filters the collection by a given key / value pair:.. code-block:: pythoncollection = Collection([{'name': 'Desk', 'price': 200},{'name': 'Chair', 'price': 100},{'name': 'Bookcase', 'price': 150},{'name': 'Door', 'price': 100},])filtered = collection.where('price', 100)filtered.all()# [#     {'name': 'Chair', 'price': 100},#     {'name': 'Door', 'price': 100}# ].. _zip:``zip()``---------The ``zip`` method merges together the values of the given listwith the values of the collection at the corresponding index:.. code-block:: pythoncollection = Collection(['Chair', 'Desk'])zipped = collection.zip([100, 200])zipped.all()# [('Chair', 100), ('Desk', 200)]