tryingsnake 0.2.6

Exception handling, the functional way.

TryingSnake

A simple, Try implementation inspired by scala.util.Try

Examples

• Wrap functions with arguments:

  >>> from tryingsnake import Try, Try_, Success, Failure
  >>> from operator import add, truediv
  >>> Try(add, 0, 1)
  Success(1)
  >>> Try(truediv, 1, 0)  # doctest:+ELLIPSIS
  Failure(ZeroDivisionError(...))

• Avoid sentinel values:

  >>> def mean_1(xs):
  ...     try:
  ...         return sum(xs) / len(xs)
  ...     except ZeroDivisionError as e:
  ...         return float("inf")  # What does it mean?
  >>> mean_1([])
  inf

  vs.

  >>> def mean_2(xs):
  ...     return sum(xs) / len(xs)
  >>> Try(mean_2, [])  # doctest:+ELLIPSIS
  Failure(ZeroDivisionError(...))
  >>> Try(mean_2, ["foo", "bar"])  # doctest:+ELLIPSIS
  Failure(TypeError(...))

• Follow the happy path:

  >>> def inc(x): return x + 1
  >>> def inv(x): return 1. / x
  
  >>> Success(1).map(inc).map(inv)
  Success(0.5)
  
  >>> Failure(Exception("e")).map(inc).map(inv)
  Failure(Exception('e',))
  
  >>> Success(-1).map(inc).map(inv)  # doctest:+ELLIPSIS
  Failure(ZeroDivisionError(...))

• Recover:

  >>> def get(url):
  ...     if "mirror" in url:
  ...         raise IOError("No address associated with hostname")
  ...     return url
  >>> mirrors = ["http://mirror1.example.com", "http://example.com"]
  >>> Try(get, mirrors[0]).recover(lambda _: get(mirrors[1]))
  Success('http://example.com')

• Let them fail:

  >>> from operator import getitem
  >>> Try(getitem, [], 0)
  Failure(IndexError('list index out of range',))
  >>> Try_.set_unhandled([IndexError])
  >>> Try(getitem, [], 0)
  Traceback (most recent call last):
      ...
  IndexError: list index out of range

• Make things (relatively) simple

  >>> import math
  >>> xs = [1.0, 0.0, "-1", -3, 2, 1 + 2j]
  >>> sqrts = [Try(math.sqrt, x) for x in xs]
  >>> [x.get() for x in sqrts if x.isSuccess]
  [1.0, 0.0, 1.4142135623730951]
  >>> def get_etype(e):
  ...     return Try(lambda x: type(x).__name__, e)
  >>> [x.recoverWith(get_etype).get() for x in sqrts if x.isFailure]
  ['TypeError', 'ValueError', 'TypeError']

Installation

pip install tryingsnake

or

easy_install tryingsnake

License

MIT, See LICENSE

FAQ

• Q: Is this project production-ready?

• A: No, and it probably won’t be.

• Q: Why to use mixedCase method names instead of lowercase recommended by PEP8?

• A: Mostly to make switching between Python and Scala code as painless as possible.