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Exception handling, the functional way.

Project Description

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.
Release History

Release History

This version
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0.2.6

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0.2.5

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0.2.4

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0.2.3

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0.2.2

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0.2.1

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0.2.0

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0.1.0

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