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Class, Duck types, Open, Memory view, Operator, Metaprogramming, Web, Profile
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‎README.md

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@@ -1068,7 +1068,7 @@ from dataclasses import make_dataclass
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#### Rest of type annotations (CPython interpreter ignores them all):
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```python
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import typing as tp, collections.abc as abc
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import collections.abc as abc, typing as tp
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<var_name>: list/set/abc.Iterable/abc.Sequence/tp.Optional[<type>] [= <obj>]
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<var_name>: dict/tuple/tp.Union[<type>, ...] [= <obj>]
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def func(<arg_name>: <type> [= <obj>]) -> <type>: ...
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### Collection
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* **Only required methods are iter() and len(). Len() should return the number of items.**
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* **This cheatsheet actually means `'<iterable>'` when it uses `'<collection>'`.**
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* **I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'. The only drawback of this decision is that a reader could think a certain function doesn't accept iterators when it does, since iterators are the only built-in objects that are iterable but are not collections.**
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* **I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'. The only drawback of this decision is that the reader could think a certain function doesn't accept iterators when it does, since iterators are the only built-in objects that are iterable but are not collections.**
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```python
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class MyCollection:
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def __init__(self, a):
@@ -1606,7 +1606,7 @@ Open
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<file>.writelines(<collection>) # Writes a coll. of strings or bytes objects.
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<file>.flush() # Flushes write buffer. Runs every 4096/8192 B.
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```
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* **Methods do not add or strip trailing newlines, even writelines().**
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* **Methods do not add or strip trailing newlines, not even writelines().**
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### Read Text from File
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```python
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Memory View
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-----------
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* **A sequence object that points to the memory of another object.**
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* **A sequence object that points to the memory of another bytes-like object.**
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* **Each element can reference a single or multiple consecutive bytes, depending on format.**
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* **Order and number of elements can be changed with slicing.**
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* **Casting only works between char and other types and uses system's sizes.**
@@ -2177,7 +2177,7 @@ product_of_elems = functools.reduce(op.mul, <collection>)
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union_of_sets = functools.reduce(op.or_, <coll_of_sets>)
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first_element = op.methodcaller('pop', 0)(<list>)
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```
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* **Binary operators require objects to have and(), or(), xor() and invert() special methods, unlike logical operators that work on all types of objects.**
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* **Bitwise operators require objects to have and(), or(), xor() and invert() special methods, unlike logical operators that work on all types of objects.**
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* **Also: `'<bool> = <bool> &|^ <bool>'` and `'<int> = <bool> &|^ <int>'`.**
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@@ -2250,7 +2250,7 @@ class MyMetaClass(type):
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* **The only difference between the examples above is that my\_meta\_class() returns a class of type type, while MyMetaClass() returns a class of type MyMetaClass.**
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### Metaclass Attribute
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**Right before a class is created it checks if it has the 'metaclass' attribute defined. If not, it recursively checks if any of his parents has it defined and eventually comes to type().**
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**Right before a class is created it checks if it has the 'metaclass' attribute defined. If not, it recursively checks if any of its parents has it defined and eventually comes to type().**
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```python
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class MyClass(metaclass=MyMetaClass):
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```python
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app = Flask(__name__)
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app.run(host=None, debug=None)
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app.run(host=None, port=None, debug=None)
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```
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* **Starts the app at `'http://localhost:5000'`. Use `'host="0.0.0.0"'` to run externally.**
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* **Install a WSGI server like [Waitress](https://flask.palletsprojects.com/en/latest/deploying/waitress/) and a HTTP server such as [Nginx](https://flask.palletsprojects.com/en/latest/deploying/nginx/) for better security.**
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### Profiling by Line
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```text
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$ pip3 install line_profiler
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$ echo "@profile
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$ echo '@profile
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def main():
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a = list(range(10000))
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b = set(range(10000))
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main()" > test.py
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main()' > test.py
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$ kernprof -lv test.py
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Line # Hits Time Per Hit % Time Line Contents
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=======================================================

‎index.html

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<body>
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<header>
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<aside>July 19, 2023</aside>
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<aside>July 22, 2023</aside>
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<a href="https://gto76.github.io" rel="author">Jure Šorn</a>
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</header>
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@@ -903,7 +903,7 @@
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&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_tuples&gt;)
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&lt;tuple&gt; = (<span class="hljs-string">'&lt;attr_name&gt;'</span>, &lt;type&gt; [, &lt;default_value&gt;])</code></pre></div>
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<div><h4 id="restoftypeannotationscpythoninterpreterignoresthemall">Rest of type annotations (CPython interpreter ignores them all):</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> typing <span class="hljs-keyword">as</span> tp, collections.abc <span class="hljs-keyword">as</span> abc
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<div><h4 id="restoftypeannotationscpythoninterpreterignoresthemall">Rest of type annotations (CPython interpreter ignores them all):</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> collections.abc <span class="hljs-keyword">as</span> abc, typing <span class="hljs-keyword">as</span> tp
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&lt;var_name&gt;: list/set/abc.Iterable/abc.Sequence/tp.Optional[&lt;type&gt;] [= &lt;obj&gt;]
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&lt;var_name&gt;: dict/tuple/tp.Union[&lt;type&gt;, ...] [= &lt;obj&gt;]
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<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">func</span><span class="hljs-params">(&lt;arg_name&gt;: &lt;type&gt; [= &lt;obj&gt;])</span> -&gt; &lt;type&gt;:</span> ...
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<div><h3 id="collection">Collection</h3><ul>
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<li><strong>Only required methods are iter() and len(). Len() should return the number of items.</strong></li>
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<li><strong>This cheatsheet actually means <code class="python hljs"><span class="hljs-string">'&lt;iterable&gt;'</span></code> when it uses <code class="python hljs"><span class="hljs-string">'&lt;collection&gt;'</span></code>.</strong></li>
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<li><strong>I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'. The only drawback of this decision is that a reader could think a certain function doesn't accept iterators when it does, since iterators are the only built-in objects that are iterable but are not collections.</strong></li>
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<li><strong>I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'. The only drawback of this decision is that the reader could think a certain function doesn't accept iterators when it does, since iterators are the only built-in objects that are iterable but are not collections.</strong></li>
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</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyCollection</span>:</span>
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<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
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self.a = a
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&lt;file&gt;.flush() <span class="hljs-comment"># Flushes write buffer. Runs every 4096/8192 B.</span>
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</code></pre>
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<ul>
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<li><strong>Methods do not add or strip trailing newlines, even writelines().</strong></li>
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<li><strong>Methods do not add or strip trailing newlines, not even writelines().</strong></li>
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</ul>
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<div><h3 id="readtextfromfile">Read Text from File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_file</span><span class="hljs-params">(filename)</span>:</span>
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<span class="hljs-keyword">with</span> open(filename, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
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<div><h2 id="memoryview"><a href="#memoryview" name="memoryview">#</a>Memory View</h2><ul>
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<li><strong>A sequence object that points to the memory of another object.</strong></li>
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<li><strong>A sequence object that points to the memory of another bytes-like object.</strong></li>
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<li><strong>Each element can reference a single or multiple consecutive bytes, depending on format.</strong></li>
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<li><strong>Order and number of elements can be changed with slicing.</strong></li>
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<li><strong>Casting only works between char and other types and uses system's sizes.</strong></li>
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first_element = op.methodcaller(<span class="hljs-string">'pop'</span>, <span class="hljs-number">0</span>)(&lt;list&gt;)
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</code></pre>
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<ul>
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<li><strong>Binary operators require objects to have and(), or(), xor() and invert() special methods, unlike logical operators that work on all types of objects.</strong></li>
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<li><strong>Bitwise operators require objects to have and(), or(), xor() and invert() special methods, unlike logical operators that work on all types of objects.</strong></li>
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<li><strong>Also: <code class="python hljs"><span class="hljs-string">'&lt;bool&gt; = &lt;bool&gt; &amp;|^ &lt;bool&gt;'</span></code> and <code class="python hljs"><span class="hljs-string">'&lt;int&gt; = &lt;bool&gt; &amp;|^ &lt;int&gt;'</span></code>.</strong></li>
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</ul>
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<div><h2 id="introspection"><a href="#introspection" name="introspection">#</a>Introspection</h2><p><strong>Inspecting code at runtime.</strong></p><div><h3 id="variables">Variables</h3><pre><code class="python language-python hljs">&lt;list&gt; = dir() <span class="hljs-comment"># Names of local variables (incl. functions).</span>
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<li><strong>Like in our case, new() can also be called directly, usually from a new() method of a child class (</strong><code class="python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__new__</span><span class="hljs-params">(cls)</span>:</span> <span class="hljs-keyword">return</span> super().__new__(cls)</code><strong>).</strong></li>
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<li><strong>The only difference between the examples above is that my_meta_class() returns a class of type type, while MyMetaClass() returns a class of type MyMetaClass.</strong></li>
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</ul>
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<div><h3 id="metaclassattribute">Metaclass Attribute</h3><p><strong>Right before a class is created it checks if it has the 'metaclass' attribute defined. If not, it recursively checks if any of his parents has it defined and eventually comes to type().</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClass</span><span class="hljs-params">(metaclass=MyMetaClass)</span>:</span>
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<div><h3 id="metaclassattribute">Metaclass Attribute</h3><p><strong>Right before a class is created it checks if it has the 'metaclass' attribute defined. If not, it recursively checks if any of its parents has it defined and eventually comes to type().</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClass</span><span class="hljs-params">(metaclass=MyMetaClass)</span>:</span>
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b = <span class="hljs-number">12345</span>
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</code></pre></div>
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<pre><code class="python language-python hljs">app = Flask(__name__)
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app.run(host=<span class="hljs-keyword">None</span>, debug=<span class="hljs-keyword">None</span>)
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app.run(host=<span class="hljs-keyword">None</span>, port=<span class="hljs-keyword">None</span>, debug=<span class="hljs-keyword">None</span>)
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</code></pre>
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<ul>
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<li><strong>Starts the app at <code class="python hljs"><span class="hljs-string">'http://localhost:5000'</span></code>. Use <code class="python hljs"><span class="hljs-string">'host="0.0.0.0"'</span></code> to run externally.</strong></li>
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</code></pre></div>
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<div><h3 id="profilingbyline">Profiling by Line</h3><pre><code class="text language-text">$ pip3 install line_profiler
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$ echo "@profile
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$ echo '@profile
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def main():
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a = list(range(10000))
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b = set(range(10000))
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main()" &gt; test.py
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main()' &gt; test.py
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$ kernprof -lv test.py
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Line # Hits Time Per Hit % Time Line Contents
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=======================================================
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<footer>
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<aside>July 19, 2023</aside>
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<aside>July 22, 2023</aside>
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<a href="https://gto76.github.io" rel="author">Jure Šorn</a>
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</footer>
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