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A function decorator for failing computations
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| from functools import (wraps) | |
| from itertools import (chain) | |
| class Failure: | |
| """Signifies a failure in a computation that was wrapped by a `@maybe` | |
| decorator.""" | |
| def __init__(self, func, fails=None, exception=None): | |
| self.name = func.__name__ | |
| self.fails = fails | |
| self.exception = exception | |
| self.trace = [] | |
| def __bool__(self): | |
| """Failures are falsy.""" | |
| return False | |
| def add_trace(self, func): | |
| self.trace.append(func.__name__) | |
| def __str__(self): | |
| msg = "Fail: " + " -> ".join(self.trace + [self.name]) | |
| if self.exception is not None: | |
| msg += "\n* {}: ".format(type(self.exception).__name__) | |
| msg += "\n ".join(l for l in str(self.exception).split('\n')) | |
| elif self.fails: | |
| msg += "\n* failed arguments:\n " | |
| msg += "\n ".join( | |
| "{} `{}` ".format(func, source) + "\n ".join( | |
| l for l in str(fail).split('\n')) | |
| for func, source, fail in self.fails) | |
| return msg | |
| def is_fail(obj): | |
| """Checks if an object is a Failure.""" | |
| return isinstance(obj, Failure) | |
| def maybe(func): | |
| """Function decorator. Makes a function failt-tolerant by wrapping | |
| the function call in a `try/except` block and checking arguments for | |
| previous failures.""" | |
| @wraps(func) | |
| def maybe_wrapped(*args, **kwargs): | |
| # filter for all failures | |
| fails = [(func.__name__, k, v) for k, v in | |
| chain(enumerate(args), kwargs.items()) | |
| if is_fail(v)] | |
| if fails: | |
| return Failure(func, fails=fails) | |
| try: | |
| result = func(*args, **kwargs) | |
| except Exception as exc: | |
| return Failure(func, exception=exc) | |
| else: | |
| if is_fail(result): | |
| result.trace.append(func) | |
| return result | |
| return maybe_wrapped |
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| from maybe import maybe, is_fail | |
| import math | |
| @maybe | |
| def reciprocal(x): | |
| return 1 / x | |
| @maybe | |
| def square_root(x): | |
| return math.sqrt(x) | |
| print(square_root(reciprocal(0))) | |
| print(square_root(reciprocal(-1))) |
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