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python-cheatsheet
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Exceptions

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Jure Šorn 5 years ago
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  1. 75
      README.md
  2. 72
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75
README.md
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@ -1306,36 +1306,63 @@ from functools import partial
LogicOp = Enum('LogicOp', {'AND': partial(lambda l, r: l and r), LogicOp = Enum('LogicOp', {'AND': partial(lambda l, r: l and r),
'OR' : partial(lambda l, r: l or r)}) 'OR' : partial(lambda l, r: l or r)})
``` ```
* **Another solution in this particular case, is to use `'and_'` and `'or_'` functions from module [operator](#operator) as values.**
Exceptions Exceptions
---------- ----------
### Basic Example
```python ```python
while True:
try:
x = int(input('Please enter a number: '))
except ValueError:
print('Oops! That was no valid number. Try again...')
else:
print('Thank you.')
break
try:
<code>
except <exception>:
<code>
```
### Complex Example
```python
try:
<code_1>
except <exception_a>:
<code_2_a>
except <exception_b>:
<code_2_b>
else:
<code_2_c>
finally:
<code_3>
```
### Catching Exceptions
```python
except <exception>:
except <exception> as <name>:
except (<exception_1>, <exception_2>, ...):
except (<exception_1>, <exception_2>, ...) as <name>:
```
* **Also catches subclasses of the exception.**
### Raising Exceptions
```python
raise <exception>
raise <exception>()
raise <exception>(<el>)
raise <exception>(<el_1>, <el_2>, ...)
``` ```
### Raising Exception
#### Useful built-in exceptions:
```python ```python
raise ValueError('A very specific message!')
raise ValueError('Argument is of right type but inappropriate value!')
raise TypeError('Argument is of wrong type!')
raise RuntimeError('None of above!')
``` ```
### Finally
#### Re-raising caught exception:
```python ```python
>>> try:
... raise KeyboardInterrupt
... finally:
... print('Goodbye, world!')
Goodbye, world!
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
KeyboardInterrupt
except <exception>:
<code>
raise
``` ```
### Common Built-in Exceptions ### Common Built-in Exceptions
@ -1361,7 +1388,15 @@ BaseException
+-- ValueError # When an argument is of right type but inappropriate value. +-- ValueError # When an argument is of right type but inappropriate value.
+-- UnicodeError # Raised when encoding/decoding strings from/to bytes fails. +-- UnicodeError # Raised when encoding/decoding strings from/to bytes fails.
``` ```
* **Appropriate built-in exceptions for user to rise are: 'ValueError', 'TypeError' and 'RuntimeError'.**
### User-defined Exceptions
```python
class MyError(Exception):
pass
class MyInputError(MyError):
pass
```
Print Print

72
index.html
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@ -1210,28 +1210,52 @@ Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, {<span class="hljs-st
LogicOp = Enum(<span class="hljs-string">'LogicOp'</span>, {<span class="hljs-string">'AND'</span>: partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">and</span> r), LogicOp = Enum(<span class="hljs-string">'LogicOp'</span>, {<span class="hljs-string">'AND'</span>: partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">and</span> r),
<span class="hljs-string">'OR'</span> : partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">or</span> r)}) <span class="hljs-string">'OR'</span> : partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">or</span> r)})
</code></pre> </code></pre>
<ul>
<li><strong>Another solution in this particular case, is to use <code class="python hljs"><span class="hljs-string">'and_'</span></code> and <code class="python hljs"><span class="hljs-string">'or_'</span></code> functions from module <a href="#operator">operator</a> as values.</strong></li>
</ul>
<h2 id="exceptions"><a href="#exceptions" name="exceptions">#</a>Exceptions</h2> <h2 id="exceptions"><a href="#exceptions" name="exceptions">#</a>Exceptions</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
<span class="hljs-keyword">try</span>:
x = int(input(<span class="hljs-string">'Please enter a number: '</span>))
<span class="hljs-keyword">except</span> ValueError:
print(<span class="hljs-string">'Oops! That was no valid number. Try again...'</span>)
<span class="hljs-keyword">else</span>:
print(<span class="hljs-string">'Thank you.'</span>)
<span class="hljs-keyword">break</span>
<h3 id="basicexample">Basic Example</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">try</span>:
&lt;code&gt;
<span class="hljs-keyword">except</span> &lt;exception&gt;:
&lt;code&gt;
</code></pre> </code></pre>
<h3 id="raisingexception">Raising Exception</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'A very specific message!'</span>)
<h3 id="complexexample">Complex Example</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">try</span>:
&lt;code_1&gt;
<span class="hljs-keyword">except</span> &lt;exception_a&gt;:
&lt;code_2_a&gt;
<span class="hljs-keyword">except</span> &lt;exception_b&gt;:
&lt;code_2_b&gt;
<span class="hljs-keyword">else</span>:
&lt;code_2_c&gt;
<span class="hljs-keyword">finally</span>:
&lt;code_3&gt;
</code></pre>
<h3 id="catchingexceptions">Catching Exceptions</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">except</span> &lt;exception&gt;:
<span class="hljs-keyword">except</span> &lt;exception&gt; <span class="hljs-keyword">as</span> &lt;name&gt;:
<span class="hljs-keyword">except</span> (&lt;exception_1&gt;, &lt;exception_2&gt;, ...):
<span class="hljs-keyword">except</span> (&lt;exception_1&gt;, &lt;exception_2&gt;, ...) <span class="hljs-keyword">as</span> &lt;name&gt;:
</code></pre> </code></pre>
<h3 id="finally">Finally</h3>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">try</span>:
<span class="hljs-meta">... </span> <span class="hljs-keyword">raise</span> KeyboardInterrupt
<span class="hljs-meta">... </span><span class="hljs-keyword">finally</span>:
<span class="hljs-meta">... </span> print(<span class="hljs-string">'Goodbye, world!'</span>)
Goodbye, world!
Traceback (most recent call last):
File <span class="hljs-string">"&lt;stdin&gt;"</span>, line <span class="hljs-number">2</span>, <span class="hljs-keyword">in</span> &lt;module&gt;
KeyboardInterrupt
<ul>
<li><strong>Also catches subclasses of the exception.</strong></li>
</ul>
<h3 id="raisingexceptions">Raising Exceptions</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">raise</span> &lt;exception&gt;
<span class="hljs-keyword">raise</span> &lt;exception&gt;()
<span class="hljs-keyword">raise</span> &lt;exception&gt;(&lt;el&gt;)
<span class="hljs-keyword">raise</span> &lt;exception&gt;(&lt;el_1&gt;, &lt;el_2&gt;, ...)
</code></pre>
<h4 id="usefulbuiltinexceptions">Useful built-in exceptions:</h4>
<pre><code class="python language-python hljs"><span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'Argument is of right type but inappropriate value!'</span>)
<span class="hljs-keyword">raise</span> TypeError(<span class="hljs-string">'Argument is of wrong type!'</span>)
<span class="hljs-keyword">raise</span> RuntimeError(<span class="hljs-string">'None of above!'</span>)
</code></pre>
<h4 id="reraisingcaughtexception">Re-raising caught exception:</h4>
<pre><code class="python language-python hljs"><span class="hljs-keyword">except</span> &lt;exception&gt;:
&lt;code&gt;
<span class="hljs-keyword">raise</span>
</code></pre> </code></pre>
<h3 id="commonbuiltinexceptions">Common Built-in Exceptions</h3> <h3 id="commonbuiltinexceptions">Common Built-in Exceptions</h3>
<pre><code class="python language-python hljs">BaseException <pre><code class="python language-python hljs">BaseException
@ -1255,9 +1279,13 @@ KeyboardInterrupt
+-- ValueError <span class="hljs-comment"># When an argument is of right type but inappropriate value.</span> +-- ValueError <span class="hljs-comment"># When an argument is of right type but inappropriate value.</span>
+-- UnicodeError <span class="hljs-comment"># Raised when encoding/decoding strings from/to bytes fails. </span> +-- UnicodeError <span class="hljs-comment"># Raised when encoding/decoding strings from/to bytes fails. </span>
</code></pre> </code></pre>
<ul>
<li><strong>Appropriate built-in exceptions for user to rise are: 'ValueError', 'TypeError' and 'RuntimeError'.</strong></li>
</ul>
<h3 id="userdefinedexceptions">User-defined Exceptions</h3>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyError</span><span class="hljs-params">(Exception)</span>:</span>
<span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyInputError</span><span class="hljs-params">(MyError)</span>:</span>
<span class="hljs-keyword">pass</span>
</code></pre>
<h2 id="print"><a href="#print" name="print">#</a>Print</h2> <h2 id="print"><a href="#print" name="print">#</a>Print</h2>
<pre><code class="python language-python hljs">print(&lt;el_1&gt;, ..., sep=<span class="hljs-string">' '</span>, end=<span class="hljs-string">'\n'</span>, file=sys.stdout, flush=<span class="hljs-keyword">False</span>) <pre><code class="python language-python hljs">print(&lt;el_1&gt;, ..., sep=<span class="hljs-string">' '</span>, end=<span class="hljs-string">'\n'</span>, file=sys.stdout, flush=<span class="hljs-keyword">False</span>)
</code></pre> </code></pre>

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