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Flexible tree data structures for organizing lists and dicts into sections.

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Flexible tree data structures for organizing lists and dicts into sections.

sections is designed to be:

  • Intuitive: Start quickly and spend less time reading the docs.

  • Scalable: Grow arbitrarily complex trees as your problem scales.

  • Flexible: Rapidly build nodes with custom attributes, properties, and methods on the fly.

  • Fast: Made with performance in mind - access lists and sub-lists/dicts in Θ(1) time in many cases. See the Performance section for the full details.

  • Reliable: Contains an exhaustive test suite and 100% code coverage.

See the full documentation at In addition to a repeat of this readme page, the docs also contain some other useful sections, in particular a References section, which more thoroughly documents all the interfacing methods for Section objects.


pip install sections
import sections

menu = sections(
    'Breakfast', 'Dinner',
    mains=['Bacon&Eggs', 'Burger'],
    sides=['HashBrown', 'Fries'],
# Resulting structure's API and the expected results:
assert menu.mains == ['Bacon&Eggs', 'Burger']
assert menu.sides == ['HashBrown', 'Fries']
assert menu['Breakfast'].main == 'Bacon&Eggs'
assert menu['Breakfast'].side == 'HashBrown'
assert menu['Dinner'].main == 'Burger'
assert menu['Dinner'].side == 'Fries'
assert menu('sides', list) == ['HashBrown', 'Fries']
assert menu('sides', dict) == {'Breakfast': 'HashBrown', 'Dinner': 'Fries'}
# root section/node:
assert isinstance(menu, sections.Section)
# child sections/nodes:
assert isinstance(menu['Breakfast'], sections.Section)
assert isinstance(menu['Dinner'], sections.Section)

Attrs: Plural/singular hybrid attributes and more

Spend less time deciding between using the singular or plural form for an attribute name:

tasks = sections('pay bill', 'clean', status=['completed', 'started'])
assert tasks.statuses == ['completed', 'started']
assert tasks['pay bill'].status == 'completed'
assert tasks['clean'].status == 'started'

If you don’t like this feature, simply turn it off as shown in the Details - Plural/singular attribute settings section.

Properties: Easily add on the fly

Properties and methods are automatically added to all nodes in a structure returned from a sections() call when passed as keyword arguments:

schedule = sections(
    'Weekdays', 'Weekend',
    hours_per_day=[[8, 8, 6, 10, 8], [4, 6]],
    hours=property(lambda self: sum(self.hours_per_day)),
assert schedule['Weekdays'].hours == 40
assert schedule['Weekend'].hours == 10
assert schedule.hours == 50

Adding properties and methods this way doesn’t affect the class definitions of Sections/nodes from other structures. See the Details - Properties/methods section for how this works.

Construction: Build gradually or all at once

Construct section-by-section, section-wise, attribute-wise, or other ways:

def demo_different_construction_techniques():
    """Example construction techniques for producing the same structure."""
    # Building section-by-section
    books = sections()
    books['LOTR'] = sections(topic='Hobbits', author='JRR Tolkien')
    books['Harry Potter'] = sections(topic='Wizards', author='JK Rowling')

    # Section-wise construction
    books = sections(
        sections('LOTR', topic='Hobbits', author='JRR Tolkien'),
        sections('Harry Potter', topic='Wizards', author='JK Rowling')

    # Attribute-wise construction
    books = sections(
        'LOTR', 'Harry Potter',
        topics=['Hobbits', 'Wizards'],
        authors=['JRR Tolkien', 'JK Rowling']

    # setattr post-construction
    books = sections(
        'LOTR', 'Harry Potter',
    books.topics = ['Hobbits', 'Wizards']
    books['LOTR'].author = 'JRR Tolkien'
    books['Harry Potter'].author = 'JK Rowling'

def demo_resulting_object_api(books):
    """Example Section structure API and expected results."""
    assert books.names == ['LOTR', 'Harry Potter']
    assert books.topics == ['Hobbits', 'Wizards']
    assert books.authors == ['JRR Tolkien', 'JK Rowling']
    assert books['LOTR'].topic == 'Hobbits'
    assert books['LOTR'].author == 'JRR Tolkien'
    assert books['Harry Potter'].topic == 'Wizards'
    assert books['Harry Potter'].author == 'JK Rowling'



Section names

The non-keyword arguments passed into a sections() call define the section names and are accessed through the attribute name. The names are used like keys in a dict to access each child section of the root Section node:

books = sections(
    'LOTR', 'Harry Potter',
    topics=['Hobbits', 'Wizards'],
    authors=['JRR Tolkien', 'JK Rowling']
assert books.names == ['LOTR', 'Harry Potter']
assert books['LOTR'].name == 'LOTR'
assert books['Harry Potter'].name == 'Harry Potter'

Names are optional, and by default, children names will be assigned as integer values corresponding to indices in an array, while a root has a default keyvalue of sections.SectionNone:

sect = sections(x=['a', 'b'])
assert sect.sections.names == [0, 1]
assert is sections.SectionNone

# the string representation of sections.SectionNone is 'section':
assert str( == 'section'

Parent names and attributes

A parent section name can optionally be provided as the first argument in a list or Section instantiation by defining it in a set (surrounding it with curly brackets). This strategy avoids an extra level of braces when instantiating Section objects. This idea applies also for defining parent attributes:

library = sections(
    {"My Bookshelf"},
    [{'Fantasy'}, 'LOTR', 'Harry Potter'],
    [{'Academic'}, 'Advanced Mathematics', 'Physics for Engineers'],
    topics=[{'All my books'},
            [{'Imaginary things'}, 'Hobbits', 'Wizards'],
            [{'School'}, 'Numbers', 'Forces']],
assert == "My Bookshelf"
assert library.sections.names == ['Fantasy', 'Academic']
assert library['Fantasy'].sections.names == ['LOTR', 'Harry Potter']
assert library['Academic'].sections.names == [
    'Advanced Mathematics', 'Physics for Engineers'
assert library['Fantasy']['Harry Potter'].name == 'Harry Potter'
assert library.topic == 'All my books'
assert library['Fantasy'].topic == 'Imaginary things'
assert library['Academic'].topic == 'School'

Return attributes as a list, dict, or iterable

Access the data in different forms with the gettype argument in Section.__call__() as follows:

menu = sections('Breakfast', 'Dinner', sides=['HashBrown', 'Fries'])

# return as list always, even if a single element is returned
assert menu('sides', list) == ['HashBrown', 'Fries']
assert menu['Breakfast']('side', list) == ['HashBrown']

# return as dict
assert menu('sides', dict) == {'Breakfast': 'HashBrown', 'Dinner': 'Fries'}
assert menu['Breakfast']('side', dict) == {'Breakfast': 'HashBrown'}

# return as iterator over elements in list (fastest method, theoretically)
for i, value in enumerate(menu('sides', iter)):
    assert value == ['HashBrown', 'Fries'][i]
for i, value in enumerate(menu['Breakfast']('side', iter)):
    assert value == ['HashBrown'][i]

See the Section.__call__() method in the References section of the docs for more options.

Set the default return type when accessing structure attributes by changing Section.default_gettype as follows:

menu = sections('Breakfast', 'Dinner', sides=['HashBrown', 'Fries'])

menu['Breakfast'].default_gettype = dict  # set for only 'Breakfast' node
assert menu.sides == ['HashBrown', 'Fries']
assert menu['Breakfast']('side') == {'Breakfast': 'HashBrown'}

menu.cls.default_gettype = dict           # set for all nodes in `menu`
assert menu('sides') == {'Breakfast': 'HashBrown', 'Dinner': 'Fries'}
assert menu['Breakfast']('side') == {'Breakfast': 'HashBrown'}

sections.Section.default_gettype = dict   # set for all structures
tasks1 = sections('pay bill', 'clean', status=['completed', 'started'])
tasks2 = sections('pay bill', 'clean', status=['completed', 'started'])
assert tasks1('statuses') == {'pay bill': 'completed', 'clean': 'started'}
assert tasks2('statuses') == {'pay bill': 'completed', 'clean': 'started'}

The above will also work for accessing attributes in the form object.attr but only if the node does not contain the attribute attr, otherwise it will return the non-iterable raw value for attr. Therefore, for consistency, access attributes using Section.__call__() like above if you wish to always receive an iterable form of the attributes.

Plural/singular attribute settings

When an attribute is not found in a Section node, both the plural and singular forms of the word are then checked to see if the node contains the attribute under those forms of the word. If they are still not found, the node will recursively repeat the same search on each of its children, concatenating the results into a list or dict. The true attribute name in each node supplied a corresponding value is whatever name was given in the keyword argument’s key (i.e. status in the example below).

If you don’t like this feature, simply turn it off using the following:

import pytest
tasks = sections('pay bill', 'clean', status=['completed', 'started'])
assert tasks.statuses == ['completed', 'started']
sections.Section.use_pluralsingular = False  # turn off for all future objs
tasks = sections('pay bill', 'clean', status=['completed', 'started'])
with pytest.raises(AttributeError):
    tasks.statuses  # this now raises an AttributeError

Note, however, that this will still traverse descendant nodes to see if they contain the requested attribute. To stop using this feature also, access attributes using the Section.get_node_attr() method instead.


Each sections() call returns a structure containing nodes of a unique class created in a class factory function, where the unique class definition contains no logic except that it inherits from the Section class. This allows properties/methods added to one structure’s class definition to not affect the class definitions of nodes from other structures.


Section structures can be visualized through the Section.deep_str() method as follows:

library = sections(
    {"My Bookshelf"},
    [{'Fantasy'}, 'LOTR', 'Harry Potter'],
    [{'Academic'}, 'Advanced Mathematics', 'Physics for Engineers'],
    topics=[{'All my books'},
            [{'Imaginary things'}, 'Hobbits', 'Wizards'],
            [{'School'}, 'Numbers', 'Forces']],


<class 'Section'> structure

'My Bookshelf' = <root, parent>
    parent = None
    children = ['Fantasy', 'Academic']
    topics = 'All my books'

'Fantasy' = <child, parent>
    parent = 'My Bookshelf'
    children = ['LOTR', 'Harry Potter']
    topics = 'Imaginary things'

'Academic' = <child, parent>
    parent = 'My Bookshelf'
    children = ['Advanced Mathematics', 'Physics for Engineers']
    topics = 'School'

'LOTR' = <child, leaf>
    parent = 'Fantasy'
    topics = 'Hobbits'

'Harry Potter' = <child, leaf>
    parent = 'Fantasy'
    topics = 'Wizards'

'Advanced Mathematics' = <child, leaf>
    parent = 'Academic'
    topics = 'Numbers'

'Physics for Engineers' = <child, leaf>
    parent = 'Academic'
    topics = 'Forces'

See the References section of the docs for more printing options.


Inheriting Section is easy, the only requirement is to call super().__init__(**kwds) at some point in __init__() like below if you override that method:

class Library(sections.Section):
    """My library class."""
    def __init__(price="Custom default value", **kwds):
        """Pass **kwds to super."""

    def genres(self):
        """A synonym for sections."""
        if self.isroot:
            return self.sections
            raise AttributeError('This library has only 1 level of genres')

    def books(self):
        """A synonym for leaves."""
        return self.leaves

    def titles(self):
        """A synonym for names."""
        return self.names

    def critique(self, impression="Haven't read it yet", rating=0):
        """Set the book price based on the impression.""" = impression
        self.price = rating * 2

library = Library(
    [{'Fantasy'}, 'LOTR', 'Harry Potter'],
    [{'Academic'}, 'Advanced Math.', 'Physics for Engineers']
assert library.genres.names == ['Fantasy', 'Academic']
assert library.books.titles == [
    'LOTR', 'Harry Potter', 'Advanced Math.', 'Physics for Engineers'
library.books['LOTR'].critique(impression='Good but too long', rating=7)
library.books['Harry Potter'].critique(
    impression="I don't like owls", rating=4)
assert library.books['LOTR'].price == 14
assert library.books['Harry Potter'].price == 8
import pytest
with pytest.raises(AttributeError):

Section.__init__() assigns the kwds values passed to it to the object attributes, and the passed kwds are generated during instantiation by a metaclass.


Each non-leaf Section node keeps a cache containing quickly readable references to attribute dicts previously parsed from manually traversing through descendant nodes in an earlier read. The caches are invalidated accordingly for modified nodes and their ancestors when the tree structure or node attribute values change.

The caches allow instant reading of sub-lists/dicts in Θ(1) time and can often make structure attribute reading faster by 5x, or even much more when the structure is rarely being modified.

However, for structures representing lists/dicts with more than 1000 - 10,000 elements, the extra memory consumption that this technique uses may start to make it not beneficial to use. It is therefore recommended to consider changing the node or structure’s class attribute use_cache to False for structures in this range or larger. This can be done as follows:

sect = sections(*[[[[[42] * 10] * 10] * 10] * 10])
sect.use_cache = False              # turn off for just the root node
sect.cls.use_cache = False          # turn off for all nodes in `sect`
sections.Section.use_cache = False  # turn off for all structures

The dict option for gettype in the Section.__call__() method is currently slower than the other options. For performance-critical uses, use the other options for gettype. Alternatively, if a dict is required just for visual printing purposes, use the faster 'full_dict' option for gettype instead. This option returns dicts with valid values with keys that also have string representations of the node names, but the raw form of the keys are references to node objects and cannot be referenced by the user through strings. See the Section.__call__() method in the References section of the docs for more details on the gettype options.

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