product_of_elems = functools.reduce(lambda out, el: out * el, <collection>)
list_of_chars = list(<str>)
```
* **For details about built-in functions sorted(), min() and max() see [sortable](#sortable).**
* **Module [operator](#operator) provides functions itemgetter() and mul() that offer the same functionality as [lambda](#lambda) expressions above.**
```python
@ -1084,6 +1085,7 @@ Duck Types
* **If eq() method is not overridden, it returns `'id(self) == id(other)'`, which is the same as `'self is other'`.**
* **That means all objects compare not equal by default.**
* **Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted.**
* **Ne() automatically works on any object that has eq() defined.**
```python
class MyComparable:
@ -1116,7 +1118,10 @@ class MyHashable:
```
### Sortable
* **With total_ordering decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods.**
* **With total_ordering decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods and the rest will be automatically generated.**
* **Functions sorted() and min() only require lt() method, while max() only requires gt(). However, it is best to define them all so that confusion doesn't arise in other contexts.**
* **When two lists, strings or dataclasses are compared, their values get compared in order until a pair of unequal values is found. The comparison of this two values is then returned. The shorter sequence is considered smaller in case of all elements being equal.**
```python
from functools import total_ordering
@ -1230,7 +1235,7 @@ True
### Collection
* **Only required methods are iter() and len().**
* **This cheatsheet actually means `'<iterable>'` when it uses `'<collection>'`.**
* **I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'.**
* **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 iterable objects that are not collections.**
@ -273,6 +273,7 @@ product_of_elems = functools.reduce(<span class="hljs-keyword">lambda</span> out
list_of_chars = list(<str>)
</code></pre>
<ul>
<li><strong>For details about built-in functions sorted(), min() and max() see <ahref="#sortable">sortable</a>.</strong></li>
<li><strong>Module <ahref="#operator">operator</a> provides functions itemgetter() and mul() that offer the same functionality as <ahref="#lambda">lambda</a> expressions above.</strong></li>
</ul>
<pre><codeclass="python language-python hljs"><list>.insert(<int>, <el>) <spanclass="hljs-comment"># Inserts item at index and moves the rest to the right.</span>
@ -1065,6 +1066,7 @@ Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span clas
<li><strong>If eq() method is not overridden, it returns <codeclass="python hljs"><spanclass="hljs-string">'id(self) == id(other)'</span></code>, which is the same as <codeclass="python hljs"><spanclass="hljs-string">'self is other'</span></code>.</strong></li>
<li><strong>That means all objects compare not equal by default.</strong></li>
<li><strong>Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted.</strong></li>
<li><strong>Ne() automatically works on any object that has eq() defined.</strong></li>
@ -1097,7 +1099,9 @@ Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span clas
<div><h3id="sortable">Sortable</h3><ul>
<li><strong>With total_ordering decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods.</strong></li>
<li><strong>With total_ordering decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods and the rest will be automatically generated.</strong></li>
<li><strong>Functions sorted() and min() only require lt() method, while max() only requires gt(). However, it is best to define them all so that confusion doesn't arise in other contexts.</strong></li>
<li><strong>When two lists, strings or dataclasses are compared, their values get compared in order until a pair of unequal values is found. The comparison of this two values is then returned. The shorter sequence is considered smaller in case of all elements being equal.</strong></li>
<li><strong>Only required methods are iter() and len().</strong></li>
<li><strong>This cheatsheet actually means <codeclass="python hljs"><spanclass="hljs-string">'<iterable>'</span></code> when it uses <codeclass="python hljs"><spanclass="hljs-string">'<collection>'</span></code>.</strong></li>
<li><strong>I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'.</strong></li>
<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 iterable objects that are not collections.</strong></li>
<div><h2id="operator"><ahref="#operator"name="operator">#</a>Operator</h2><p><strong>Module of functions that provide the functionality of operators.</strong></p><pre><codeclass="python language-python hljs"><spanclass="hljs-keyword">from</span> operator <spanclass="hljs-keyword">import</span> add, sub, mul, truediv, floordiv, mod, pow, neg, abs
<spanclass="hljs-keyword">from</span> operator <spanclass="hljs-keyword">import</span> eq, ne, lt, le, gt, ge
<div><h2id="introspection"><ahref="#introspection"name="introspection">#</a>Introspection</h2><p><strong>Inspecting code at runtime.</strong></p><div><h3id="variables">Variables</h3><pre><codeclass="python language-python hljs"><list> = dir() <spanclass="hljs-comment"># Names of local variables (incl. functions).</span>
<dict> = vars() <spanclass="hljs-comment"># Dict of local variables. Also locals().</span>
'<strong>For details about built-in functions sorted(), min() and max() see <a href="#sortable">sortable</a>.</strong>':'<strong>For details about built-in functions sorted(), min() and max() see sortable (p. 16).</strong>',
'<strong>Module <a href="#operator">operator</a> provides functions itemgetter() and mul() that offer the same functionality as <a href="#lambda">lambda</a> expressions above.</strong>':'<strong>Module \'operator\' (p. 31) provides functions itemgetter() and mul() that offer the same functionality as lambda expressions (p. 11) above.</strong>',
'<strong>Adding <code class="python hljs"><span class="hljs-string">\'!r\'</span></code> before the colon converts object to string by calling its <a href="#class">repr()</a> method.</strong>':'<strong>Adding <code class="python hljs"><span class="hljs-string">\'!r\'</span></code> before the colon converts object to string by calling its repr() method (p. 14).</strong>',
'<strong>It can be any <a href="#callable">callable</a>, but is usually implemented as a function that returns a <a href="#closure">closure</a>.</strong>':'<strong>It can be any callable (p. 17), but is usually implemented as a function that returns a closure (p. 12).</strong>',
'<strong>Default_factory can be any <a href="#callable">callable</a>.</strong>':'<strong>Default_factory can be any callable (p. 17).</strong>',
'<strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">\'<attr_name>: list = []\'</span></code> would make a list that is shared among all instances. Its \'default_factory\' argument can be any <a href="#callable">callable</a>.</strong>':'<strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">\'<attr_name>: list = []\'</span></code> would make a list that is shared among all instances. Its \'default_factory\' argument can be any callable (p. 17).</strong>',
'<strong>Sequence iterators returned by the <a href="#iterator">iter()</a> function, such as list_iterator and set_iterator.</strong>':'<strong>Sequence iterators returned by the iter() function, such as list_iterator and set_iterator (p. 3).</strong>',
'<strong>Objects returned by the <a href="#itertools">itertools</a> module, such as count, repeat and cycle.</strong>':'<strong>Objects returned by the itertools module, such as count, repeat and cycle (p. 3).</strong>',
'<strong>Generators returned by the <a href="#generator">generator functions</a> and <a href="#comprehensions">generator expressions</a>.</strong>':'<strong>Generators returned by the generator functions (p. 4) and generator expressions (p. 11).</strong>',
Jure Šorn
2 years ago