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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"

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<head>

<title>Function caching</title>

</head>

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<h1>Function caching</h1>

Function caching allows us to cache the return values of a function

depending on the arguments. It can save time when an I/O bound function

is periodically called with the same arguments. Before Python 3.2 we had

to write a custom implementation. In Python 3.2+ there is an

<code class="docutils literal">lru_cache</code> decorator which allows us to quickly cache and uncache the

return values of a function.

Let’s see how we can use it in Python 3.2+ and the versions before it.

<h2>Python 3.2+</h2>

Let’s implement a ficonnaci calculator and use <code class="docutils literal">lru_cache</code>.

<div class="code python highlight-python"><div class="highlight"><pre>from functools import lru_cache

@lru_cache(maxsize=32)

def fib(n):

if n < 2:

return n

return fib(n-1) + fib(n-2)

>>> print([fib(n) for n in range(10)])

# Output: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

</pre></div>

</div>

The <code class="docutils literal">maxsize</code> argument tells <code class="docutils literal">lru_cache</code> about how many recent

return values to cache.

We can easily uncache the return values as well by using:

<div class="code python highlight-python"><div class="highlight"><pre>fib.cache_clear()

</pre></div>

</div>

<h2>Python 2+</h2>

There are a couple of ways to achieve the same effect. You can create

any type of caching machanism. It entirely depends upon your needs. Here

is a generic cache:

<div class="code python highlight-python"><div class="highlight"><pre>from functools import wraps

def memoize(function):

memo = {}

@wraps(function)

def wrapper(*args):

if args in memo:

return memo[args]

else:

rv = function(*args)

memo[args] = rv

return rv

return wrapper

@memoize

def fibonacci(n):

if n < 2: return n

return fibonacci(n - 1) + fibonacci(n - 2)

fibonacci(25)

</pre></div>

</div>

<a class="reference external" href="https://www.caktusgroup.com/blog/2015/06/08/testing-client-side-applications-django-post-mortem/">Here</a> [https://www.caktusgroup.com/blog/2015/06/08/testing-client-side-applications-django-post-mortem/]

is a fine article by Caktus Group in which they caught a bug in Django

which occured due to lru_cache. It’s an interesting read. Do check it

out.

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