cs.deco 20190307.2

Assorted decorator functions.

Assorted decorator functions.

Function cached(*da, **dkw)

Decorator to cache the result of a method and keep a revision counter for changes. The revision supports the @revised decorator.

This decorator may be used in 2 modes. Directly:

@cached
def method(self, ...)

or indirectly:

@cached(poll_delay=0.25)
def method(self, ...)

Optional keyword arguments:

• attr_name: the basis name for the supporting attributes. Default: the name of the method.
• poll_delay: minimum time between polls; after the first access, subsequent accesses before the poll_delay has elapsed will return the cached value. Default: None, meaning no poll delay.
• sig_func: a signature function, which should be significantly cheaper than the method. If the signature is unchanged, the cached value will be returned. The signature function expects the instance (self) as its first parameter. Default: None, meaning no signature function; the first computed value will be kept and never updated.
• unset_value: the value to return before the method has been called successfully. Default: None.

If the method raises an exception, this will be logged and the method will return the previously cached value.

An example use of this decorator might be to keep a "live" configuration data structure, parsed from a configuration file which might be modified after the program starts. One might provide a signature function which called os.stat() on the file to check for changes before invoking a full read and parse of the file.

Function decorator(deco)

Wrapper for decorator functions to support optional keyword arguments.

Examples:

@decorator
def dec(func, **dkw):
  ...
@dec
def func1(...):
  ...
@dec(foo='bah')
def func2(...):
  ...

Function strable(*da, **dkw)

Decorator for functions which may accept a str instead of their core type.

Parameters:

• func: the function to decorate
• open_func: the "open" factory to produce the core type form the string if a string is provided; the default is the builtin "open" function

The usual (and default) example is a function to process an open file, designed to be handed a file object but which may be called with a filename. If the first argument is a str then that file is opened and the function called with the open file.

Examples:

@strable
def count_lines(f):
  return len(line for line in f)

class Recording:
  "Class representing a video recording."
  ...
@strable
def process_video(r, open_func=Recording):
  ... do stuff with `r` as a Recording instance ...