Backtest your Trading Systems with Python

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Abstract

const boundFn = fn.bind(this); Object.defineProperty(this, key, { value: boundFn, configurable: true, writable: true, }); return boundFn; }, }; }

class MyComponent { constructor(props) { this.props = props; } @autobind handleClick() { console.log(this.props); } }</pre></div>In this example, the decorator is used to decorate the function so that it automatically binds this when called and returns a new function. This way, after instantiating , you don’t need to manually bind this when calling the function.<code>autobindhandleClickMyComponentthis.handleClick()</code><h1 id="3ffe">Logging</h1>Decorators can be used to record logs, including printing information such as function calls, function execution times, etc.<div id="1a70"><pre>function log(target, name, descriptor) { const originalMethod = descriptor.value;

descriptor.value = function (...args) { console.log(Function ${name} called with ${args}); const start = performance.now(); const result = originalMethod.apply(this, args); const duration = performance.now() - start; console.log(Function ${name} completed in ${duration}ms); return result; }; return descriptor } class MyClass { @log myMethod(arg1, arg2) { return arg1 + arg2; } }

const obj = new MyClass(); obj.myMethod(1, 2); // Output: // Function myMethod called with 1,2 // Function myMethod completed in 0.013614237010165215ms</pre></div><h1 id="aff7">Authentication authentication</h1>Decorators can also be used to check a user’s authentication status and permissions to prevent unauthorized users from accessing sensitive data or performing actions on a regular basis.<div id="be1a"><pre>function authorization(target, name, descriptor) { const originalMethod = descriptor.value;

descriptor.value = function(...args) { if (!this.isAuthenticated()) { console.error('Access denied! Not authenticated'); return; } if (!this.hasAccessTo(name)) { console.error(Access denied! User does not have permission to ${name}); return; } return originalMethod.apply(this, args); }; return descriptor; }

class MyApi { isAuthenticated() { // perform authentication check return true; } hasAccessTo(endpoint) { // perform authorization check return true; } @authorization getUsers() { // return users data } @authorization deleteUser(id) { // delete user with id } }</pre></div><h1 id="646e">Cache</h1>Decorators can also be used to cache the execution results of functions to avoid double evaluation.<div id="5257"><pre>function memoize(target, name, descriptor) { const originalMethod = descriptor.value; const cache = new Map();

descriptor.value = function (...args) { const cacheKey = args.toString(); if (cache.has(cacheKey)) { console.log(cache hit: ${cacheKey}); return cache.get(cacheKey); } const result = originalMethod.apply(this, args); console.log(cache miss: ${cacheKey}); cache.set(cacheKey, result); return result; }; return descriptor; }

class

Options

MyMath { @memoize calculate(num) { console.log('calculate called'); return num * 2; } }

const math = new MyMath(); console.log(math.calculate(10)); // Output: // calculate called // cache miss: 10 // 20 console.log(math.calculate(10)); // Output: // cache hit: 10 // 20</pre></div><h1 id="57d9">Aspect-oriented programming</h1>Decorators can be used to implement facet-oriented programming, that is, to add functionality at runtime without modifying the original code.<div id="bc4d"><pre>function validate(target, name, descriptor) { const originalMethod = descriptor.value;

descriptor.value = function (...args) { const isValid = args.every(arg => typeof arg === 'string' && arg.length > 0); if (!isValid) { console.error('Invalid arguments'); return; } return originalMethod.apply(this, args); }; return descriptor; }

class MyForm { @validate submit(name, email, message) { // submit the form } }

const form = new MyForm(); form.submit('', '[email protected]', 'Hello world'); // Output: Invalid arguments</pre></div><h1 id="c8da">Reversible decorators</h1>Decorators can also be applied in reversible scenes, for example, you can add a reversible decorator to modify function behavior.<div id="b868"><pre>function reverse(target, name, descriptor) { const originalMethod = descriptor.value;

descriptor.value = function (...args) { args.reverse(); return originalMethod.apply(this, args); }; return descriptor; } class MyMath { @reverse calculate(num1, num2) { return num1 + num2; } }

const math = new MyMath(); console.log(math.calculate(1, 2)); // Output: 3 console.log(math.calculate.reversed(1, 2)); // Output: 3</pre></div><h1 id="2ddc">Automatic type checking</h1>Decorators can be applied to automatic type checking, for example, you can add a decorator to ensure that the type of a function parameter is correct.<div id="a63a"><pre>function checkType(expectedType) { return function(target, name, descriptor) { const originalMethod = descriptor.value;

descriptor.<span class="hljs-property">value</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">...args</span>) {
      <span class="hljs-keyword">const</span> invalidArgs = args.<span class="hljs-title function_">filter</span>(<span class="hljs-function"><span class="hljs-params">arg</span> =&gt;</span> <span class="hljs-keyword">typeof</span> arg !== expectedType);
      <span class="hljs-keyword">if</span> (invalidArgs.<span class="hljs-property">length</span> &gt; <span class="hljs-number">0</span>) {
        <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(<span class="hljs-string">`Invalid arguments: <span class="hljs-subst">${invalidArgs}</span>`</span>);
        <span class="hljs-keyword">return</span>;
      }
      <span class="hljs-keyword">return</span> originalMethod.<span class="hljs-title function_">apply</span>(<span class="hljs-variable language_">this</span>, args);
    };
    <span class="hljs-keyword">return</span> descriptor;
  }

}

class MyMath { @checkType('number') add(num1, num2) { return num1 + num2; } }

const math = new MyMath(); math.add(1, '2'); // Output: Invalid arguments: 2</pre></div>More content at <a href="https://plainenglish.io/">PlainEnglish.io</a>.Sign up for our <a href="http://newsletter.plainenglish.io/">free weekly newsletter</a>. Follow us on <a href="https://twitter.com/inPlainEngHQ">Twitter</a>, <a href="https://www.linkedin.com/company/inplainenglish/">LinkedIn</a>, <a href="https://www.youtube.com/channel/UCtipWUghju290NWcn8jhyAw">YouTube</a>, and <a href="https://discord.gg/GtDtUAvyhW">Discord</a>.Interested in scaling your software startup? Check out <a href="https://circuit.ooo?utm=publication-post-cta">Circuit</a>.</article></body>

Backtest your Trading Systems with Python — Custom Analyzers

How an Analyzer Works in Backtrader

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Using an Analyzer

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