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Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/library/functools.rst | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst index 75c9d41..e981bcd 100644 --- a/Doc/library/functools.rst +++ b/Doc/library/functools.rst @@ -62,16 +62,26 @@ The :mod:`functools` module defines the following functions: Example:: class DataSet: + def __init__(self, sequence_of_numbers): - self._data = sequence_of_numbers + self._data = tuple(sequence_of_numbers) @cached_property def stdev(self): return statistics.stdev(self._data) - @cached_property - def variance(self): - return statistics.variance(self._data) + The mechanics of :func:`cached_property` are somewhat different from + :func:`property`. A regular property blocks attribute writes unless a + setter is defined. In contrast, a *cached_property* allows writes. + + The *cached_property* decorator only runs on lookups and only when an + attribute of the same name doesn't exist. When it does run, the + *cached_property* writes to the attribute with the same name. Subsequent + attribute reads and writes take precedence over the *cached_property* + method and it works like a normal attribute. + + The cached value can be cleared by deleting the attribute. This + allows the *cached_property* method to run again. Note, this decorator interferes with the operation of :pep:`412` key-sharing dictionaries. This means that instance dictionaries |