[Tut] Python bytes() Function - Printable Version

[Tut] Python bytes() Function - Printable Version

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[Tut] Python bytes() Function - xSicKxBot - 12-08-2020

Python bytes() Function

<div>Python’s built-in <code>bytes(source)</code> function creates an immutable <code>bytes</code> object initialized as defined in the function argument <code>source</code>. A bytes object is like a string but it uses only byte characters consisting of a sequence of 8-bit integers in the range <code>0<=x<256</code>. The returned byte object is immutable—you cannot change it after creation. If you plan to change the contents, use the <code><a href="https://blog.finxter.com/python-bytearray-function/" title="Python bytearray() Function" target="_blank" rel="noreferrer noopener">bytearray()</a></code> method to create a mutable <code>bytearray</code> object. 
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Here’s a minimal example that creates a <code>byte</code> from three integers stored in a list:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> bytes([1, 2, 3])
b'\x01\x02\x03'</pre>
The prefix <code>\x</code> escape sequence means the next two characters are interpreted as hex character codes. For instance, the hex code <code>\x01</code> is the same as <code>chr(0x01)=16*0+1=1</code> that’s simply a start of heading <code>SOH</code> character. (<a href="https://stackoverflow.com/questions/2672326/what-does-a-leading-x-mean-in-a-python-string-xaa" target="_blank" rel="noreferrer noopener" title="https://stackoverflow.com/questions/2672326/what-does-a-leading-x-mean-in-a-python-string-xaa">source</a>, <a href="https://blog.finxter.com/ascii-table/" title="ASCII Table" target="_blank" rel="noreferrer noopener">ASCII table</a>)
<pre class="wp-block-preformatted">Syntax: <code>bytes([source[, encoding[, errors]]])</code></pre>
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<tbody>
<tr>
<td>Argument</td>
<td><code>source</code> (Optional)</td>
<td>Allows you to initialize the <code>byte</code> in four different ways (from simple to more complex):
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> integer –> array has this size and is initialized with 0 bytes: >>> <code>bytes(4) b'\x00\x00\x00\x00'</code>
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> iterable –> integers in the range <code>0 <= x < 256</code> are initial byte contents: >>> <code>bytes([1, 2, 3]) b'\x01\x02\x03'</code>
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> string and you provide the encoding (and optionally, errors) arguments –> <code>bytes()</code> converts string to bytes using <a href="https://docs.python.org/3/library/stdtypes.html#str.encode"><code>str.encode()</code></a>: <code>>>> bytes('hi', 'UTF-8') b'hi'</code>
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> object implementing the <a href="https://docs.python.org/3/c-api/buffer.html#bufferobjects">buffer interface</a> –> initializes the byte object via a read-only object buffer.</td>
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<td>Argument</td>
<td><code>encoding</code> (Optional)</td>
<td>The encoding used in case you provide a string argument. Example: <code>'UTF-8'</code>. </td>
</tr>
<tr>
<td>Argument</td>
<td><code>errors</code> (Optional)</td>
<td>The action to take when the encoding conversion fails. Only makes sense if <code>source</code> argument is a string.</td>
</tr>
<tr>
<td>Return Value</td>
<td><code>byte</code></td>
<td>Returns a new object of type byte—a sequence of bytes that is immutable. For a mutable version, consider using the <code><a href="https://blog.finxter.com/python-bytearray-function/" title="Python bytearray() Function">bytearray()</a></code> function. <img src="https://s.w.org/images/core/emoji/13.0.0/72x72/2b50.png" alt="⭐" class="wp-smiley" style="height: 1em; max-height: 1em;" /> Without an optional argument, it returns a byte object with one byte 0: <code>>>> bytes() b''</code></td>
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Here are some basic usages of the function:
<pre class="wp-block-preformatted">Input : <code>bytes(4)</code>
Output : <code><code>b'\x00\x00\x00\x00'</code></code> Input : <code>bytes([1, 2, 3])</code>
Output : <code><code>b'\x01\x02\x03'</code></code> Input : <code>bytes('hi', 'UTF-8')</code>
Output : <code>b'hi'</code></pre>
Want to learn more? We’re going to dive into more examples next!
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<h2>Create Bytes Object From Single Integer Argument — Examples </h2>
The following code shows you how to use the <code>bytes()</code> function on simple integer arguments.
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group=""># Single Integer Input Argument
print(bytes())
print(bytes(2))
print(bytes(4)) '''
b''
b'\x00\x00'
b'\x00\x00\x00\x00' '''</pre>
If you provide only one input argument, it uses this input argument to determine how many bytes should be created. It just uses bytes with value 0, in byte notation <code>x00</code> to fill the <code>byte</code>.
<h2>Create Bytes Object From Iterable of Integers — Examples</h2>
You can also provide an iterable argument to obtain a new byte object:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group=""># Iterable Input Argument
print(bytes([1, 1, 1]))
print(bytes([14]))
print(bytes({9, 8, 7})) '''
b'\x01\x01\x01'
b'\x0e'
b'\x08\t\x07' '''
</pre>
The iterable must consist of a number of integers between 0 and 256. If you fail to do so, Python will throw a ValueError:
<h2>How to Fix “ValueError: byte must be in range(0, 256)”</h2>
If you use the <code>bytes()</code> function on an iterable that contains at least one integer greater than the maximum number representable by 8 bits, namely 256, or smaller than 0, Python will throw a <code>ValueError: byte must be in range(0, 256)</code>. You can fix it by ensuring that each number in your iterable can actually be represented by 8 bits and falls into the interval 0 to 256. 
Here’s an example of the ValueError where you use a number larger or equal than 256:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> bytes([999])
Traceback (most recent call last): File "<pyshell#15>", line 1, in <module> bytes([999])
ValueError: bytes must be in range(0, 256)</pre>
Another example when using a number smaller than 0:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> bytes([-10])
Traceback (most recent call last): File "<pyshell#16>", line 1, in <module> bytes([-10])
ValueError: bytes must be in range(0, 256)</pre>
Fix it by modifying the numbers to lie within the interval 0 to 256:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> bytes([255])
b'\xff'</pre>
<h2>Summary</h2>
Python’s built-in function <code>bytes()</code> allows you to initialize the <code>byte</code> in four different ways (from simple to more complex):
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> integer –> array has this size and is initialized with 0 bytes:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> bytes(4)
b'\x00\x00\x00\x00'</pre>
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> iterable –> integers in the range <code>0 <= x < 256</code> are initial byte contents:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> bytes([1, 2, 3])
b'\x01\x02\x03'</pre>
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> string and you provide the encoding (and optionally, errors) arguments –> <code>bytes()</code> converts string to bytes using <a href="https://docs.python.org/3/library/stdtypes.html#str.encode"><code>str.encode()</code></a>:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> bytes('hi', 'UTF-8')
b'hi'</pre>
<img src="https://s.w.org/images/core/emoji/13.0.0/72x72/1f40d.png" alt="?" class="wp-smiley" style="height: 1em; max-height: 1em;" /> object implementing the <a href="https://docs.python.org/3/c-api/buffer.html#bufferobjects">buffer interface</a> –> initializes the byte object via a read-only object buffer.
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