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python-cheatsheet
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Jure Šorn 5 years ago
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  1. 29
      README.md
  2. 29
      index.html

29
README.md
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@ -929,21 +929,22 @@ class <name>:
* **Return value of repr() should be unambiguous and of str() readable.**
* **If only repr() is defined, it will also be used for str().**
#### Str() is used by:
#### Str() use cases:
```python
print(<el>)
f'{<el>}'
print(f'{<el>}')
raise Exception(<el>)
logging.debug(<el>)
csv.writer(<file>).writerow([<el>])
```
#### Repr() is used by:
#### Repr() use cases:
```python
print([<el>])
f'{<el>!r}'
print(f'{<el>!r}')
>>> <el>
loguru.logger.exception()
Z = dataclasses.make_dataclass('Z', ['a']); print(Z(<el>))
```
### Constructor Overloading
@ -1502,12 +1503,14 @@ def write_to_pickle_file(filename, an_object):
SQLite
------
**Server-less database engine that stores each database into separate file.**
```python
import sqlite3
db = sqlite3.connect('<path>') # Also ':memory:'.
...
db.close()
```
* **New database will be created if path doesn't exist.**
### Read
```python
@ -1516,7 +1519,7 @@ if cursor:
<tuple> = cursor.fetchone() # First row.
<list> = cursor.fetchall() # Remaining rows.
```
* **Returned values can be of type str, int, float or bytes.**
* **Returned values can be of type str, int, float, bytes or None.**
### Write
```python
@ -1526,10 +1529,20 @@ db.commit()
### Placeholders
```python
db.execute('<query>', <list/tuple>) # Replaces '?' in query with value.
db.execute('<query>', <dict/namedtuple>) # Replaces ':<key>' with value.
db.execute('<query>', <list/tuple>) # Replaces '?'s in query with values.
db.execute('<query>', <dict/namedtuple>) # Replaces ':<key>'s with values.
db.executemany('<query>', <coll_of_above>) # Runs execute() many times.
```
* **Passed values can be of type str, int, float, bytes, None, bool, datetime.date or datetime.datetme.**
### MySQL
```python
# $ pip3 install mysql-connector
from mysql import connector
db = connector.connect(host=<str>, user=<str>, password=<str>, database=<str>)
cursor = db.cursor()
cursor.execute('<query>')
```
* **Passed values can be of type str, int, float, bytes, bool, datetime.date and datetime.datetme.**
Bytes

29
index.html
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@ -883,18 +883,19 @@ creature = Creature(Point(<span class="hljs-number">0</span>, <span class="hljs
<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>
</ul>
<h4 id="strisusedby">Str() is used by:</h4>
<h4 id="strusecases">Str() use cases:</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>
print(<span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;}</span>'</span>)
<span class="hljs-keyword">raise</span> Exception(&lt;el&gt;)
logging.debug(&lt;el&gt;)
csv.writer(&lt;file&gt;).writerow([&lt;el&gt;])
</code></pre>
<h4 id="reprisusedby">Repr() is used by:</h4>
<h4 id="reprusecases">Repr() use cases:</h4>
<pre><code class="python language-python hljs">print([&lt;el&gt;])
<span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;!r}</span>'</span>
print(<span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;!r}</span>'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>&lt;el&gt;
loguru.logger.exception()
Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span class="hljs-string">'a'</span>]); print(Z(&lt;el&gt;))
</code></pre>
<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>
@ -1323,11 +1324,15 @@ value = args.&lt;name&gt;
pickle.dump(an_object, file)
</code></pre>
<h2 id="sqlite"><a href="#sqlite" name="sqlite">#</a>SQLite</h2>
<p><strong>Server-less database engine that stores each database into separate file.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sqlite3
db = sqlite3.connect(<span class="hljs-string">'&lt;path&gt;'</span>) <span class="hljs-comment"># Also ':memory:'.</span>
...
db.close()
</code></pre>
<ul>
<li><strong>New database will be created if path doesn't exist.</strong></li>
</ul>
<h3 id="read">Read</h3>
<pre><code class="python language-python hljs">cursor = db.execute(<span class="hljs-string">'&lt;query&gt;'</span>)
<span class="hljs-keyword">if</span> cursor:
@ -1335,19 +1340,27 @@ db.close()
&lt;list&gt; = cursor.fetchall() <span class="hljs-comment"># Remaining rows.</span>
</code></pre>
<ul>
<li><strong>Returned values can be of type str, int, float or bytes.</strong></li>
<li><strong>Returned values can be of type str, int, float, bytes or None.</strong></li>
</ul>
<h3 id="write">Write</h3>
<pre><code class="python language-python hljs">db.execute(<span class="hljs-string">'&lt;query&gt;'</span>)
db.commit()
</code></pre>
<h3 id="placeholders">Placeholders</h3>
<pre><code class="python language-python hljs">db.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;list/tuple&gt;) <span class="hljs-comment"># Replaces '?' in query with value.</span>
db.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;dict/namedtuple&gt;) <span class="hljs-comment"># Replaces ':&lt;key&gt;' with value.</span>
<pre><code class="python language-python hljs">db.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;list/tuple&gt;) <span class="hljs-comment"># Replaces '?'s in query with values.</span>
db.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;dict/namedtuple&gt;) <span class="hljs-comment"># Replaces ':&lt;key&gt;'s with values.</span>
db.executemany(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;coll_of_above&gt;) <span class="hljs-comment"># Runs execute() many times.</span>
</code></pre>
<ul>
<li><strong>Passed values can be of type str, int, float, bytes, bool, datetime.date and datetime.datetme.</strong></li>
<li><strong>Passed values can be of type str, int, float, bytes, None, bool, datetime.date or datetime.datetme.</strong></li>
</ul>
<h3 id="mysql">MySQL</h3>
<pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install mysql-connector</span>
<span class="hljs-keyword">from</span> mysql <span class="hljs-keyword">import</span> connector
db = connector.connect(host=&lt;str&gt;, user=&lt;str&gt;, password=&lt;str&gt;, database=&lt;str&gt;)
cursor = db.cursor()
cursor.execute(<span class="hljs-string">'&lt;query&gt;'</span>)
</code></pre>
<h2 id="bytes"><a href="#bytes" name="bytes">#</a>Bytes</h2>
<p><strong>Bytes object is an immutable sequence of single bytes. Mutable version is called 'bytearray'.</strong></p>
<pre><code class="python language-python hljs">&lt;bytes&gt; = <span class="hljs-string">b'&lt;str&gt;'</span> <span class="hljs-comment"># Only accepts ASCII characters and \x00 - \xff.</span>

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