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Imports, Class

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@ -816,6 +816,8 @@ player = Player(point, direction) # Returns its instance.
Imports Imports
------- -------
**Mechanism that makes code in one module available to another module.**
```python ```python
import <module> # Imports a built-in or '<module>.py'. import <module> # Imports a built-in or '<module>.py'.
import <package> # Imports a built-in or '<package>/__init__.py'. import <package> # Imports a built-in or '<package>/__init__.py'.
@ -826,7 +828,6 @@ import <package>.<module> # Imports a built-in or '<package>/<module>.py'.
* **Running `'import <package>'` does not automatically provide access to the package's modules unless they are explicitly imported in its init script.** * **Running `'import <package>'` does not automatically provide access to the package's modules unless they are explicitly imported in its init script.**
* **Location of the file that is passed to python command serves as a root of all local imports.** * **Location of the file that is passed to python command serves as a root of all local imports.**
* **For relative imports use `'from .[…][<pkg/module>[.…]] import <obj>'`.** * **For relative imports use `'from .[…][<pkg/module>[.…]] import <obj>'`.**
* **To install your package go to its parent dir, add 'import setuptools; setuptools.setup()' to setup.py, '[options]' and 'packages = &lt;dir&gt;' to setup.cfg, and run `'pip3 install -e .'`.**
Closure Closure
@ -951,8 +952,10 @@ def add(x, y):
Class Class
----- -----
**A template for creating user-defined objects.**
```python ```python
class <name>:
class MyClass:
def __init__(self, a): def __init__(self, a):
self.a = a self.a = a
def __str__(self): def __str__(self):
@ -969,6 +972,12 @@ class <name>:
* **If only repr() is defined, it will also be used for str().** * **If only repr() is defined, it will also be used for str().**
* **Methods decorated with `'@staticmethod'` do not receive 'self' nor 'cls' as their first arg.** * **Methods decorated with `'@staticmethod'` do not receive 'self' nor 'cls' as their first arg.**
```python
>>> obj = MyClass(1)
>>> obj.a, str(obj), repr(obj)
(1, '1', 'MyClass(1)')
```
#### Expressions that call the str() method: #### Expressions that call the str() method:
```python ```python
print(<el>) print(<el>)
@ -987,13 +996,6 @@ Z = dataclasses.make_dataclass('Z', ['a']); print/str/repr(Z(<el>))
>>> <el> >>> <el>
``` ```
### Constructor Overloading
```python
class <name>:
def __init__(self, a=None):
self.a = a
```
### Inheritance ### Inheritance
```python ```python
class Person: class Person:
@ -1006,7 +1008,7 @@ class Employee(Person):
self.staff_num = staff_num self.staff_num = staff_num
``` ```
### Multiple Inheritance
#### Multiple inheritance:
```python ```python
class A: pass class A: pass
class B: pass class B: pass
@ -1019,26 +1021,6 @@ class C(A, B): pass
[<class 'C'>, <class 'A'>, <class 'B'>, <class 'object'>] [<class 'C'>, <class 'A'>, <class 'B'>, <class 'object'>]
``` ```
### Property
**Pythonic way of implementing getters and setters.**
```python
class Person:
@property
def name(self):
return ' '.join(self._name)
@name.setter
def name(self, value):
self._name = value.split()
```
```python
>>> person = Person()
>>> person.name = '\t Guido van Rossum \n'
>>> person.name
'Guido van Rossum'
```
### Type Annotations ### Type Annotations
* **They add type hints to variables, arguments and functions (`'def f() -> <type>:'`).** * **They add type hints to variables, arguments and functions (`'def f() -> <type>:'`).**
* **Hints are used by type checkers like [mypy](https://pypi.org/project/mypy/), data validation libraries such as [Pydantic](https://pypi.org/project/pydantic/) and lately also by [Cython](https://pypi.org/project/Cython/) compiler. However, they are not enforced by CPython interpreter.** * **Hints are used by type checkers like [mypy](https://pypi.org/project/mypy/), data validation libraries such as [Pydantic](https://pypi.org/project/pydantic/) and lately also by [Cython](https://pypi.org/project/Cython/) compiler. However, they are not enforced by CPython interpreter.**
@ -1072,6 +1054,26 @@ class <class_name>:
<tuple> = ('<attr_name>', <type> [, <default_value>]) <tuple> = ('<attr_name>', <type> [, <default_value>])
``` ```
### Property
**Pythonic way of implementing getters and setters.**
```python
class Person:
@property
def name(self):
return ' '.join(self._name)
@name.setter
def name(self, value):
self._name = value.split()
```
```python
>>> person = Person()
>>> person.name = '\t Guido van Rossum \n'
>>> person.name
'Guido van Rossum'
```
### Slots ### Slots
**Mechanism that restricts objects to attributes listed in 'slots', reduces their memory footprint.** **Mechanism that restricts objects to attributes listed in 'slots', reduces their memory footprint.**

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@ -684,18 +684,18 @@ direction = Direction.N <span class="hljs-comment">#
Player = make_dataclass(<span class="hljs-string">'Player'</span>, [<span class="hljs-string">'loc'</span>, <span class="hljs-string">'dir'</span>]) <span class="hljs-comment"># Creates a class.</span> Player = make_dataclass(<span class="hljs-string">'Player'</span>, [<span class="hljs-string">'loc'</span>, <span class="hljs-string">'dir'</span>]) <span class="hljs-comment"># Creates a class.</span>
player = Player(point, direction) <span class="hljs-comment"># Returns its instance.</span> player = Player(point, direction) <span class="hljs-comment"># Returns its instance.</span>
</code></pre> </code></pre>
<div><h2 id="imports"><a href="#imports" name="imports">#</a>Imports</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> &lt;module&gt; <span class="hljs-comment"># Imports a built-in or '&lt;module&gt;.py'.</span>
<div><h2 id="imports"><a href="#imports" name="imports">#</a>Imports</h2><p><strong>Mechanism that makes code in one module available to another module.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> &lt;module&gt; <span class="hljs-comment"># Imports a built-in or '&lt;module&gt;.py'.</span>
<span class="hljs-keyword">import</span> &lt;package&gt; <span class="hljs-comment"># Imports a built-in or '&lt;package&gt;/__init__.py'.</span> <span class="hljs-keyword">import</span> &lt;package&gt; <span class="hljs-comment"># Imports a built-in or '&lt;package&gt;/__init__.py'.</span>
<span class="hljs-keyword">import</span> &lt;package&gt;.&lt;module&gt; <span class="hljs-comment"># Imports a built-in or '&lt;package&gt;/&lt;module&gt;.py'.</span> <span class="hljs-keyword">import</span> &lt;package&gt;.&lt;module&gt; <span class="hljs-comment"># Imports a built-in or '&lt;package&gt;/&lt;module&gt;.py'.</span>
</code></pre></div> </code></pre></div>
<ul> <ul>
<li><strong>Package is a collection of modules, but it can also define its own objects.</strong></li> <li><strong>Package is a collection of modules, but it can also define its own objects.</strong></li>
<li><strong>On a filesystem this corresponds to a directory of Python files with an optional init script.</strong></li> <li><strong>On a filesystem this corresponds to a directory of Python files with an optional init script.</strong></li>
<li><strong>Running <code class="python hljs"><span class="hljs-string">'import &lt;package&gt;'</span></code> does not automatically provide access to the package's modules unless they are explicitly imported in its init script.</strong></li> <li><strong>Running <code class="python hljs"><span class="hljs-string">'import &lt;package&gt;'</span></code> does not automatically provide access to the package's modules unless they are explicitly imported in its init script.</strong></li>
<li><strong>Location of the file that is passed to python command serves as a root of all local imports.</strong></li> <li><strong>Location of the file that is passed to python command serves as a root of all local imports.</strong></li>
<li><strong>For relative imports use <code class="python hljs"><span class="hljs-string">'from .[…][&lt;pkg/module&gt;[.…]] import &lt;obj&gt;'</span></code>.</strong></li> <li><strong>For relative imports use <code class="python hljs"><span class="hljs-string">'from .[…][&lt;pkg/module&gt;[.…]] import &lt;obj&gt;'</span></code>.</strong></li>
<li><strong>To install your package go to its parent dir, add 'import setuptools; setuptools.setup()' to setup.py, '[options]' and 'packages = &lt;dir&gt;' to setup.cfg, and run <code class="python hljs"><span class="hljs-string">'pip3 install -e .'</span></code>.</strong></li>
</ul> </ul>
<div><h2 id="closure"><a href="#closure" name="closure">#</a>Closure</h2><p><strong>We have/get a closure in Python when a nested function references a value of its enclosing function and then the enclosing function returns the nested function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_multiplier</span><span class="hljs-params">(a)</span>:</span> <div><h2 id="closure"><a href="#closure" name="closure">#</a>Closure</h2><p><strong>We have/get a closure in Python when a nested function references a value of its enclosing function and then the enclosing function returns the nested function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_multiplier</span><span class="hljs-params">(a)</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(b)</span>:</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(b)</span>:</span>
@ -800,7 +800,7 @@ player = Player(point, direction) <span class="hljs-comment">#
<ul> <ul>
<li><strong>Using only <code class="python hljs"><span class="hljs-string">'@debug'</span></code> to decorate the add() function would not work here, because debug would then receive the add() function as a 'print_result' argument. Decorators can however manually check if the argument they received is a function and act accordingly.</strong></li> <li><strong>Using only <code class="python hljs"><span class="hljs-string">'@debug'</span></code> to decorate the add() function would not work here, because debug would then receive the add() function as a 'print_result' argument. Decorators can however manually check if the argument they received is a function and act accordingly.</strong></li>
</ul> </ul>
<div><h2 id="class"><a href="#class" name="class">#</a>Class</h2><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">name</span>&gt;:</span>
<div><h2 id="class"><a href="#class" name="class">#</a>Class</h2><p><strong>A template for creating user-defined objects.</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>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.a = a self.a = a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
@ -814,11 +814,16 @@ player = Player(point, direction) <span class="hljs-comment">#
<span class="hljs-keyword">return</span> cls.__name__ <span class="hljs-keyword">return</span> cls.__name__
</code></pre></div> </code></pre></div>
<ul> <ul>
<li><strong>Return value of repr() should be unambiguous and of str() readable.</strong></li> <li><strong>Return value of repr() should be unambiguous and of str() readable.</strong></li>
<li><strong>If only repr() is defined, it will also be used for str().</strong></li> <li><strong>If only repr() is defined, it will also be used for str().</strong></li>
<li><strong>Methods decorated with <code class="python hljs"><span class="hljs-string">'@staticmethod'</span></code> do not receive 'self' nor 'cls' as their first arg.</strong></li> <li><strong>Methods decorated with <code class="python hljs"><span class="hljs-string">'@staticmethod'</span></code> do not receive 'self' nor 'cls' as their first arg.</strong></li>
</ul> </ul>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>obj = MyClass(<span class="hljs-number">1</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>obj.a, str(obj), repr(obj)
(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>, <span class="hljs-string">'MyClass(1)'</span>)
</code></pre>
<div><h4 id="expressionsthatcallthestrmethod">Expressions that call the str() method:</h4><pre><code class="python language-python hljs">print(&lt;el&gt;) <div><h4 id="expressionsthatcallthestrmethod">Expressions that call the str() method:</h4><pre><code class="python language-python hljs">print(&lt;el&gt;)
<span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;}</span>'</span> <span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;}</span>'</span>
logging.warning(&lt;el&gt;) logging.warning(&lt;el&gt;)
@ -833,11 +838,6 @@ Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span clas
<span class="hljs-meta">&gt;&gt;&gt; </span>&lt;el&gt; <span class="hljs-meta">&gt;&gt;&gt; </span>&lt;el&gt;
</code></pre></div> </code></pre></div>
<div><h3 id="constructoroverloading">Constructor Overloading</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">name</span>&gt;:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a=<span class="hljs-keyword">None</span>)</span>:</span>
self.a = a
</code></pre></div>
<div><h3 id="inheritance">Inheritance</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span> <div><h3 id="inheritance">Inheritance</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name)</span>:</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name)</span>:</span>
self.name = name self.name = name
@ -848,7 +848,7 @@ Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span clas
self.staff_num = staff_num self.staff_num = staff_num
</code></pre></div> </code></pre></div>
<div><h3 id="multipleinheritance">Multiple Inheritance</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">A</span>:</span> <span class="hljs-keyword">pass</span>
<div><h4 id="multipleinheritance">Multiple inheritance:</h4><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">A</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">B</span>:</span> <span class="hljs-keyword">pass</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">B</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">C</span><span class="hljs-params">(A, B)</span>:</span> <span class="hljs-keyword">pass</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">C</span><span class="hljs-params">(A, B)</span>:</span> <span class="hljs-keyword">pass</span>
</code></pre></div> </code></pre></div>
@ -857,22 +857,6 @@ Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span clas
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>C.mro() <pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>C.mro()
[&lt;<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">C</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">A</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">B</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">object</span>'&gt;] [&lt;<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">C</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">A</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">B</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">object</span>'&gt;]
</span></code></pre> </span></code></pre>
<div><h3 id="property">Property</h3><p><strong>Pythonic way of implementing getters and setters.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
<span class="hljs-meta"> @property</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">name</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> <span class="hljs-string">' '</span>.join(self._name)
<span class="hljs-meta"> @name.setter</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">name</span><span class="hljs-params">(self, value)</span>:</span>
self._name = value.split()
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>person = Person()
<span class="hljs-meta">&gt;&gt;&gt; </span>person.name = <span class="hljs-string">'\t Guido van Rossum \n'</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>person.name
<span class="hljs-string">'Guido van Rossum'</span>
</code></pre>
<div><h3 id="typeannotations">Type Annotations</h3><ul> <div><h3 id="typeannotations">Type Annotations</h3><ul>
<li><strong>They add type hints to variables, arguments and functions (<code class="python hljs"><span class="hljs-string">'def f() -&gt; &lt;type&gt;:'</span></code>).</strong></li> <li><strong>They add type hints to variables, arguments and functions (<code class="python hljs"><span class="hljs-string">'def f() -&gt; &lt;type&gt;:'</span></code>).</strong></li>
<li><strong>Hints are used by type checkers like <a href="https://pypi.org/project/mypy/">mypy</a>, data validation libraries such as <a href="https://pypi.org/project/pydantic/">Pydantic</a> and lately also by <a href="https://pypi.org/project/Cython/">Cython</a> compiler. However, they are not enforced by CPython interpreter.</strong></li> <li><strong>Hints are used by type checkers like <a href="https://pypi.org/project/mypy/">mypy</a>, data validation libraries such as <a href="https://pypi.org/project/pydantic/">Pydantic</a> and lately also by <a href="https://pypi.org/project/Cython/">Cython</a> compiler. However, they are not enforced by CPython interpreter.</strong></li>
@ -903,6 +887,22 @@ Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span clas
<pre><code class="python language-python hljs">&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_attribute_names&gt;) <pre><code class="python language-python hljs">&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_attribute_names&gt;)
&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_tuples&gt;) &lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_tuples&gt;)
&lt;tuple&gt; = (<span class="hljs-string">'&lt;attr_name&gt;'</span>, &lt;type&gt; [, &lt;default_value&gt;])</code></pre> &lt;tuple&gt; = (<span class="hljs-string">'&lt;attr_name&gt;'</span>, &lt;type&gt; [, &lt;default_value&gt;])</code></pre>
<div><h3 id="property">Property</h3><p><strong>Pythonic way of implementing getters and setters.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
<span class="hljs-meta"> @property</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">name</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> <span class="hljs-string">' '</span>.join(self._name)
<span class="hljs-meta"> @name.setter</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">name</span><span class="hljs-params">(self, value)</span>:</span>
self._name = value.split()
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>person = Person()
<span class="hljs-meta">&gt;&gt;&gt; </span>person.name = <span class="hljs-string">'\t Guido van Rossum \n'</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>person.name
<span class="hljs-string">'Guido van Rossum'</span>
</code></pre>
<div><h3 id="slots">Slots</h3><p><strong>Mechanism that restricts objects to attributes listed in 'slots', reduces their memory footprint.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClassWithSlots</span>:</span> <div><h3 id="slots">Slots</h3><p><strong>Mechanism that restricts objects to attributes listed in 'slots', reduces their memory footprint.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClassWithSlots</span>:</span>
__slots__ = [<span class="hljs-string">'a'</span>] __slots__ = [<span class="hljs-string">'a'</span>]
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>

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