Pure-func helps to write pure functions in python
Project description
Pure-func is a decorator that helps writing pure functions in python.
In python it is impossible to determine if a function is pure for certain. Even writing a static-analysis that gets the most cases right is very hard. Therefore pure-func checks purity at run-time in the spirit of python. Usually pure-func even speeds your function up, since it employs memoization to help comparing the current state of the function to a past state: Hopefully it has no state.
To ensure the performance is good when memoization doesn’t improve speed, the purity is checked exponentially less over time as pure-func gains confidence in the function.
Pure-func also ensures that the input to the function is immutable and therefore work best with pyrsistent.
Pure-func will break your program if there is hidden state in can’t detect. In this case you should fix your program.
It can also cause exponential more work if the lru-cache doesn’t take effect at all. In this case you might consider wrapping your function only for unit-testing.
def pure_func(maxsize=128, typed=False, base=2)
Check if the function has no side-effects using sampling.
Pure-func check
The distance between checks is base to the power of checks in function calls. Assuming base=2 on third check it will be check again after 8 calls. So it will take exponentially longer after every check for the next check to occur.
Least-recently-used cache
If maxsize is set to None, the LRU features are disabled and the cache can grow without bound.
If typed is True, arguments of different types will be cached separately. For example, f(3.0) and f(3) will be treated as distinct calls with distinct results.
Arguments to the cached function must be hashable.
View the cache statistics named tuple (hits, misses, maxsize, currsize) with f.cache_info(). Clear the cache and statistics with f.cache_clear(). Access the underlying function with f.__wrapped__.
See: Wikipedia
Performance
Plain fibonacci: 5702887 (took 1.86400 seconds)
Fibonacci with pure_func: 5702887 (took 0.00020 seconds)
Plain mergesort (took 0.29755 seconds)
Mergesort with pure_func (took 0.51440 seconds)Release history Release notifications | RSS feed
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