Python functools.cache and lru_cache for memoization

<p>Expensive computations (tag normalization regex compilation, settings lookups, configuration parsing) run repeatedly with the same inputs. Need simple memoization without external caching infrastructure.</p>

<p>Use <code>functools.cache</code> for in-process memoization of pure functions:</p> <div class="highlight"><pre><span></span><code><span class="kn">import</span><span class="w"> </span><span class="nn">functools</span> <span class="kn">import</span><span class="w"> </span><span class="nn">re</span> <span class="kn">from</span><span class="w"> </span><span class="nn">typing</span><span class="w"> </span><span class="kn">import</span> <span class="n">Callable</span> <span class="c1"># functools.cache (Python 3.9+) — unlimited cache, equivalent to lru_cache(maxsize=None)</span> <span class="nd">@functools</span><span class="o">.</span><span class="n">cache</span> <span class="k">def</span><span class="w"> </span><span class="nf">get_tag_pattern</span><span class="p">()</span> <span class="o">-&gt;</span> <span class="n">re</span><span class="o">.</span><span class="n">Pattern</span><span class="p">:</span> <span class="c1"># Compiled once, cached forever</span> <span class="k">return</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s1">'^[a-z0-9][a-z0-9._-]{0,48}[a-z0-9]$|^[a-z0-9]$'</span><span class="p">)</span> <span class="nd">@functools</span><span class="o">.</span><span class="n">cache</span> <span class="k">def</span><span class="w"> </span><span class="nf">normalize_tag_cached</span><span class="p">(</span><span class="n">raw</span><span class="p">:</span> <span class="nb">str</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="nb">str</span><span class="p">:</span> <span class="k">return</span> <span class="n">raw</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span><span class="o">.</span><span class="n">lower</span><span class="p">()[:</span><span class="mi">50</span><span class="p">]</span> <span class="c1"># lru_cache with max size (bounded memory)</span> <span class="nd">@functools</span><span class="o">.</span><span class="n">lru_cache</span><span class="p">(</span><span class="n">maxsize</span><span class="o">=</span><span class="mi">256</span><span class="p">)</span> <span class="k">def</span><span class="w"> </span><span class="nf">get_domain_for_tag</span><span class="p">(</span><span class="n">tag</span><span class="p">:</span> <span class="nb">str</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="nb">str</span><span class="p">:</span> <span class="c1"># Expensive lookup — cached for last 256 unique tags</span> <span class="k">return</span> <span class="n">DOMAIN_MAPPING</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">tag</span><span class="p">,</span> <span class="s1">'general'</span><span class="p">)</span> <span class="c1"># Cache with typed=True (treats int and float args as different)</span> <span class="nd">@functools</span><span class="o">.</span><span class="n">lru_cache</span><span class="p">(</span><span class="n">maxsize</span><span class="o">=</span><span class="mi">128</span><span class="p">,</span> <span class="n">typed</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="k">def</span><span class="w"> </span><span class="nf">wilson_score_cached</span><span class="p">(</span><span class="n">upvotes</span><span class="p">:</span> <span class="nb">int</span><span class="p">,</span> <span class="n">total</span><span class="p">:</span> <span class="nb">int</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="nb">float</span><span class="p">:</span> <span class="k">if</span> <span class="n">total</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span> <span class="k">return</span> <span class="mf">0.0</span> <span class="n">p</span> <span class="o">=</span> <span class="n">upvotes</span> <span class="o">/</span> <span class="n">total</span> <span class="n">z</span> <span class="o">=</span> <span class="mf">1.9600</span> <span class="n">n</span> <span class="o">=</span> <span class="n">total</span> <span class="k">return</span> <span class="p">(</span><span class="n">p</span> <span class="o">+</span> <span class="n">z</span><span class="o">*</span><span class="n">z</span><span class="o">/</span><span class="p">(</span><span class="mi">2</span><span class="o">*</span><span class="n">n</span><span class="p">)</span> <span class="o">-</span> <span class="n">z</span> <span class="o">*</span> <span class="p">((</span><span class="n">p</span><span class="o">*</span><span class="p">(</span><span class="mi">1</span><span class="o">-</span><span class="n">p</span><span class="p">)</span><span class="o">+</span><span class="n">z</span><span class="o">*</span><span class="n">z</span><span class="o">/</span><span class="p">(</span><span class="mi">4</span><span class="o">*</span><span class="n">n</span><span class="p">))</span><span class="o">/</span><span class="n">n</span><span class="p">)</span><span class="o">**</span><span class="mf">0.5</span><span class="p">)</span> <span class="o">/</span> <span class="p">(</span><span class="mi">1</span> <span class="o">+</span> <span class="n">z</span><span class="o">*</span><span class="n">z</span><span class="o">/</span><span class="n">n</span><span class="p">)</span> <span class="c1"># Method caching with cache_info</span> <span class="nb">print</span><span class="p">(</span><span class="n">wilson_score_cached</span><span class="o">.</span><span class="n">cache_info</span><span class="p">())</span> <span class="c1"># hits, misses, maxsize, currsize</span> <span class="n">wilson_score_cached</span><span class="o">.</span><span class="n">cache_clear</span><span class="p">()</span> <span class="c1"># clear when needed</span> <span class="c1"># For class methods — cache_info() works differently</span> <span class="k">class</span><span class="w"> </span><span class="nc">TagValidator</span><span class="p">:</span> <span class="nd">@functools</span><span class="o">.</span><span class="n">cached_property</span> <span class="k">def</span><span class="w"> </span><span class="nf">pattern</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">re</span><span class="o">.</span><span class="n">Pattern</span><span class="p">:</span> <span class="c1"># Computed once per instance, on first access</span> <span class="k">return</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s1">'^[a-z0-9._-]+$'</span><span class="p">)</span> <span class="k">def</span><span class="w"> </span><span class="nf">validate</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">tag</span><span class="p">:</span> <span class="nb">str</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="nb">bool</span><span class="p">:</span> <span class="k">return</span> <span class="nb">bool</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">pattern</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="n">tag</span><span class="p">))</span> </code></pre></div> <p><code>functools.cache</code> is simpler but unbounded — use only for functions with limited unique inputs. <code>lru_cache</code> evicts least-recently-used entries at <code>maxsize</code>. <code>cached_property</code> is for instance properties computed once. Thread-safe in CPython but not guaranteed across Python implementations.</p>