===============================
PyMaybe
===============================
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A Python implementation of the Maybe pattern.
Installation
------------
::
pip install pymaybe
Getting Started
---------------
::
from pymaybe import maybe
first_name = maybe(deep_hash)['account']['user_profile']['first_name'].or_else("<unknown>")
Documentation
-------------
Maybe monad is a programming pattern that allows to treat None values that same way as non-none values.
This is done by wrapping the value, which may or may not be None to, a wrapper class.
The implementation includes two classes: *Maybe* and *Something*.
*Something* represents a value while *Nothing* represents a None value.
There's also a method *maybe* which wraps a regular value and and returns *Something* or *Nothing* instance.
::
>>> maybe("I'm a value")
"I'm a value"
>>> maybe(None);
None
Both *Something* and *Nothing* implement 4 methods allowing you to test their real value: *is_some*, *is_none*, *get* and *or_else*
::
>>> maybe("I'm a value").is_some()
True
>>> maybe("I'm a value").is_none()
False
>>> maybe(None).is_some()
False
>>> maybe(None).is_none()
True
>>> maybe("I'm a value").get()
"I'm a value"
>>> maybe("I'm a value").or_else(lambda: "No value")
"I'm a value"
>>> maybe(None).get()
Traceback (most recent call last):
...
Exception: No such element
>>> maybe(None).or_else(lambda: "value")
'value'
>>> maybe(None).or_else("value")
'value'
In addition, *Something* and *Nothing* implement the Python magic methods allowing you to treat them as dictionaries:
::
>>> nested_dict = maybe(nested_dict)
>>> nested_dict['store']['name']
'MyStore'
>>> nested_dict['store']['address']
None
>>> nested_dict['store']['address']['street'].or_else('No Address Specified')
'No Address Specified'
All other method calls on *Something* are forwarded to its real *value*:
::
>>> maybe('VALUE').lower()
'value'
>>> maybe(None).invalid().method().or_else('unknwon')
'unknwon'
Examples & Use Cases
--------------------
The Maybe pattern helps you avoid nasty try..except blocks.
Consider the following code:
::
try:
url = rss.load_feeds()[0].url.domain
except (TypeError, IndexError, KeyError, AttributeError):
url = "planetpython.org"
With Maybe you could simply do:
::
url = maybe(rss).load_feeds()[0]['url'].domain.or_else("planetpython.org")
Getting the current logged in user's name.
Without maybe:
::
def get_user_zipcode():
address = getattr(request.user, 'address', None)
if address:
return getattr(address, 'zipcode', '')
return ''
With maybe:
::
def get_user_zipcode():
return maybe(request.user).address.zipcode.or_else('')
Further Reading
---------------
* `Option (Scala) <http://www.scala-lang.org/api/current/scala/Option.html>`_
* `Maybe (Java) <https://github.com/npryce/maybe-java>`_
* `Maybe pattern (Python recipe) <http://code.activestate.com/recipes/577248-maybe-pattern/>`_
* `Data.Maybe (Haskell) <http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Maybe.html>`_
* `Maybe (Ruby) <https://github.com/bhb/maybe>`_
Copyright and License
---------------------
Copyright 2015 - `Eran Kampf <http://www.developerzen.com>`_
* Free software: BSD license
* Documentation: https://pymaybe.readthedocs.org.
* Code is hosted on `GitHub <http://www.github.com/ekampf/pymaybe>`_
History
-------
0.1.0 (2015-01-11)
---------------------
* First release on PyPI.
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