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193 lines
6.1 KiB
193 lines
6.1 KiB
Metadata-Version: 2.1
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Name: traitlets
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Version: 5.0.4
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Summary: Traitlets Python configuration system
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Home-page: https://github.com/ipython/traitlets
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Author: IPython Development Team
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Author-email: ipython-dev@python.org
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License: BSD
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Project-URL: Documentation, https://traitlets.readthedocs.io/
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Project-URL: Funding, https://numfocus.org/
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Project-URL: Source, https://github.com/ipython/traitlets
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Project-URL: Tracker, https://github.com/ipython/traitlets/issues
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Keywords: Interactive,Interpreter,Shell,Web
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Platform: Linux
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Platform: Mac OS X
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Platform: Windows
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Classifier: Intended Audience :: Developers
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Classifier: Intended Audience :: System Administrators
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Classifier: Intended Audience :: Science/Research
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Classifier: License :: OSI Approved :: BSD License
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Classifier: Programming Language :: Python
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Classifier: Programming Language :: Python :: 3
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Requires-Python: >=3.7
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Description-Content-Type: text/markdown
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Requires-Dist: ipython-genutils
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Provides-Extra: test
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Requires-Dist: pytest ; extra == 'test'
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# Traitlets
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[](https://travis-ci.org/ipython/traitlets)
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[](https://traitlets.readthedocs.io/en/latest/?badge=latest)
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|---------------|----------------------------------------|
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| **home** | https://github.com/ipython/traitlets |
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| **pypi-repo** | https://pypi.org/project/traitlets/ |
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| **docs** | https://traitlets.readthedocs.io/ |
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| **license** | Modified BSD License |
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Traitlets is a pure Python library enabling:
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- the enforcement of strong typing for attributes of Python objects
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(typed attributes are called *"traits"*);
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- dynamically calculated default values;
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- automatic validation and coercion of trait attributes when attempting a
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change;
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- registering for receiving notifications when trait values change;
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- reading configuring values from files or from command line
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arguments - a distinct layer on top of traitlets, so you may use
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traitlets without the configuration machinery.
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Its implementation relies on the [descriptor](https://docs.python.org/howto/descriptor.html)
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pattern, and it is a lightweight pure-python alternative of the
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[*traits* library](http://code.enthought.com/pages/traits.html).
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Traitlets powers the configuration system of IPython and Jupyter
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and the declarative API of IPython interactive widgets.
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## Installation
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For a local installation, make sure you have
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[pip installed](https://pip.pypa.io/en/stable/installing/) and run:
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```bash
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pip install traitlets
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```
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For a **development installation**, clone this repository, change into the
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`traitlets` root directory, and run pip:
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```bash
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git clone https://github.com/ipython/traitlets.git
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cd traitlets
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pip install -e .
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```
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## Running the tests
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```bash
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pip install "traitlets[test]"
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py.test traitlets
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```
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## Usage
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Any class with trait attributes must inherit from `HasTraits`.
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For the list of available trait types and their properties, see the
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[Trait Types](https://traitlets.readthedocs.io/en/latest/trait_types.html)
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section of the documentation.
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### Dynamic default values
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To calculate a default value dynamically, decorate a method of your class with
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`@default({traitname})`. This method will be called on the instance, and
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should return the default value. In this example, the `_username_default`
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method is decorated with `@default('username')`:
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```Python
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import getpass
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from traitlets import HasTraits, Unicode, default
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class Identity(HasTraits):
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username = Unicode()
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@default('username')
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def _username_default(self):
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return getpass.getuser()
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```
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### Callbacks when a trait attribute changes
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When a trait changes, an application can follow this trait change with
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additional actions.
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To do something when a trait attribute is changed, decorate a method with
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[`traitlets.observe()`](https://traitlets.readthedocs.io/en/latest/api.html?highlight=observe#traitlets.observe).
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The method will be called with a single argument, a dictionary which contains
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an owner, new value, old value, name of the changed trait, and the event type.
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In this example, the `_num_changed` method is decorated with ``@observe(`num`)``:
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```Python
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from traitlets import HasTraits, Integer, observe
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class TraitletsExample(HasTraits):
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num = Integer(5, help="a number").tag(config=True)
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@observe('num')
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def _num_changed(self, change):
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print("{name} changed from {old} to {new}".format(**change))
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```
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and is passed the following dictionary when called:
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```Python
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{
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'owner': object, # The HasTraits instance
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'new': 6, # The new value
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'old': 5, # The old value
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'name': "foo", # The name of the changed trait
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'type': 'change', # The event type of the notification, usually 'change'
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}
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```
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### Validation and coercion
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Each trait type (`Int`, `Unicode`, `Dict` etc.) may have its own validation or
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coercion logic. In addition, we can register custom cross-validators
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that may depend on the state of other attributes. For example:
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```Python
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from traitlets import HasTraits, TraitError, Int, Bool, validate
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class Parity(HasTraits):
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value = Int()
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parity = Int()
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@validate('value')
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def _valid_value(self, proposal):
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if proposal['value'] % 2 != self.parity:
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raise TraitError('value and parity should be consistent')
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return proposal['value']
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@validate('parity')
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def _valid_parity(self, proposal):
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parity = proposal['value']
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if parity not in [0, 1]:
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raise TraitError('parity should be 0 or 1')
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if self.value % 2 != parity:
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raise TraitError('value and parity should be consistent')
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return proposal['value']
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parity_check = Parity(value=2)
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# Changing required parity and value together while holding cross validation
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with parity_check.hold_trait_notifications():
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parity_check.value = 1
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parity_check.parity = 1
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```
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However, we **recommend** that custom cross-validators don't modify the state
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of the HasTraits instance.
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### Release build:
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```bash
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$ pip install pep517
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$ python -m pep517.build .
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```
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