* **Only required method for iterable is iter(), that should return an iterator of its contents.**
* **Contains() is automatically generated whenever iter() is present.**
* **Only required method for iterable is iter(). It should return an iterator of its contents.**
* **Contains() automatically works on any object that has iter() defined.**
```python
class MyIterable:
def __init__(self, a):
@ -1192,58 +1192,69 @@ True
```
### Collection
* **Every collection is also an iterable.**
* **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.**
```python
class MyCollection:
def __init__(self, a):
self.a = a
def __iter__(self):
for el in self.a:
yield el
def __contains__(self, el):
return el in self.a
def __len__(self):
return len(self.a)
def __iter__(self):
for el in self.a:
yield el
```
### Sequence
* **Every sequence is also a collection.**
* **Iter() and reversed() are automatically generated whenever getitem() is present.**
* **Only required methods are len() and getitem().**
* **Iter(), contains() and reversed() automatically work on any object that has getitem() defined.**
```python
class MySequence:
def __init__(self, a):
self.a = a
def __getitem__(self, i):
return self.a[i]
def __iter__(self):
for el in self.a:
yield el
def __contains__(self, el):
return el in self.a
def __len__(self):
return len(self.a)
def __getitem__(self, i):
return self.a[i]
def __reversed__(self):
return reversed(self.a)
```
### Collections.abc.Sequence
* **It's a richer interface than the basic sequence.**
* **Extending it generates contains(), iter(), reversed(), index(), and count().**
* **Extending it generates iter(), contains(), reversed(), index(), and count().**
* **Unlike `'abc.Iterable'` and `'abc.Collection'`, it is not a duck type. That's why `'issubclass(MySequence, collections.abc.Sequence)'` would return 'False' even if it had all the methods defined.**
```python
class MyAbcSequence(collections.abc.Sequence):
def __init__(self, a):
self.a = a
def __getitem__(self, i):
return self.a[i]
def __len__(self):
return len(self.a)
def __getitem__(self, i):
return self.a[i]
```
#### Table of the methods that each (duck) type provides:
@ -1105,56 +1105,67 @@ con = sqlite3.connect(<span class="hljs-string">'<path>'</span>); <span c
</code></pre>
<h3id="collection">Collection</h3>
<ul>
<li><strong>Every collection is also an iterable.</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>It's a richer interface than the basic sequence.</strong></li>
<li><strong>Extending it generates contains(), iter(), reversed(), index(), and count().</strong></li>
<li><strong>Extending it generates iter(), contains(), reversed(), index(), and count().</strong></li>
<li><strong>Unlike <codeclass="python hljs"><spanclass="hljs-string">'abc.Iterable'</span></code> and <codeclass="python hljs"><spanclass="hljs-string">'abc.Collection'</span></code>, it is not a duck type. That's why <codeclass="python hljs"><spanclass="hljs-string">'issubclass(MySequence, collections.abc.Sequence)'</span></code> would return 'False' even if it had all the methods defined.</strong></li>
Jure Šorn
5 years ago