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 <section id="module-array">
<h1>8.6. <a class="reference internal" href="#module-array" title="array: Space efficient arrays of uniformly typed numeric values."><code class="xref py py-mod docutils literal notranslate">array</code></a> — Efficient arrays of numeric values<a class="headerlink" href="#module-array" title="Permalink to this headline">¶</a></h1>
This module defines an object type which can compactly represent an array of
basic values: characters, integers, floating point numbers. Arrays are sequence
types and behave very much like lists, except that the type of objects stored in
them is constrained. The type is specified at object creation time by using a
type code, which is a single character. The following type codes are
defined:
<table class="docutils align-default">
<colgroup>
<col style="width: 16%" />
<col style="width: 23%" />
<col style="width: 28%" />
<col style="width: 33%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head">Type code</th>
<th class="head">C Type</th>
<th class="head">Python Type</th>
<th class="head">Minimum size in bytes</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><code class="docutils literal notranslate">'c'</code></td>
<td>char</td>
<td>character</td>
<td>1</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'b'</code></td>
<td>signed char</td>
<td>int</td>
<td>1</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">'B'</code></td>
<td>unsigned char</td>
<td>int</td>
<td>1</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'u'</code></td>
<td>Py_UNICODE</td>
<td>Unicode character</td>
<td>2 (see note)</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">'h'</code></td>
<td>signed short</td>
<td>int</td>
<td>2</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'H'</code></td>
<td>unsigned short</td>
<td>int</td>
<td>2</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">'i'</code></td>
<td>signed int</td>
<td>int</td>
<td>2</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'I'</code></td>
<td>unsigned int</td>
<td>long</td>
<td>2</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">'l'</code></td>
<td>signed long</td>
<td>int</td>
<td>4</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'L'</code></td>
<td>unsigned long</td>
<td>long</td>
<td>4</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">'f'</code></td>
<td>float</td>
<td>float</td>
<td>4</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">'d'</code></td>
<td>double</td>
<td>float</td>
<td>8</td>
</tr>
</tbody>
</table>
<div class="admonition note">
Note
The <code class="docutils literal notranslate">'u'</code> typecode corresponds to Python’s unicode character. On narrow
Unicode builds this is 2-bytes, on wide builds this is 4-bytes.
</div>
The actual representation of values is determined by the machine architecture
(strictly speaking, by the C implementation). The actual size can be accessed
through the <code class="xref py py-attr docutils literal notranslate">itemsize</code> attribute. The values stored for <code class="docutils literal notranslate">'L'</code> and
<code class="docutils literal notranslate">'I'</code> items will be represented as Python long integers when retrieved,
because Python’s plain integer type cannot represent the full range of C’s
unsigned (long) integers.
The module defines the following type:
<dl class="py class">
<dt class="sig sig-object py" id="array.array">
class array.array(typecode[, initializer])<a class="headerlink" href="#array.array" title="Permalink to this definition">¶</a></dt>
<dd>A new array whose items are restricted by typecode, and initialized
from the optional initializer value, which must be a list, string, or iterable
over elements of the appropriate type.
<div class="versionchanged">
Changed in version 2.4: Formerly, only lists or strings were accepted.
</div>
If given a list or string, the initializer is passed to the new array’s
<a class="reference internal" href="#array.array.fromlist" title="array.array.fromlist"><code class="xref py py-meth docutils literal notranslate">fromlist()</code></a>, <a class="reference internal" href="#array.array.fromstring" title="array.array.fromstring"><code class="xref py py-meth docutils literal notranslate">fromstring()</code></a>, or <a class="reference internal" href="#array.array.fromunicode" title="array.array.fromunicode"><code class="xref py py-meth docutils literal notranslate">fromunicode()</code></a> method (see below)
to add initial items to the array. Otherwise, the iterable initializer is
passed to the <a class="reference internal" href="#array.array.extend" title="array.array.extend"><code class="xref py py-meth docutils literal notranslate">extend()</code></a> method.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="array.ArrayType">
array.ArrayType<a class="headerlink" href="#array.ArrayType" title="Permalink to this definition">¶</a></dt>
<dd>Obsolete alias for <a class="reference internal" href="#array.array" title="array.array"><code class="xref py py-class docutils literal notranslate">array</code></a>.
</dd></dl>

Array objects support the ordinary sequence operations of indexing, slicing,
concatenation, and multiplication. When using slice assignment, the assigned
value must be an array object with the same type code; in all other cases,
<code class="xref py py-exc docutils literal notranslate">TypeError</code> is raised. Array objects also implement the buffer interface,
and may be used wherever buffer objects are supported.
The following data items and methods are also supported:
<dl class="py attribute">
<dt class="sig sig-object py" id="array.array.typecode">
array.typecode<a class="headerlink" href="#array.array.typecode" title="Permalink to this definition">¶</a></dt>
<dd>The typecode character used to create the array.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="array.array.itemsize">
array.itemsize<a class="headerlink" href="#array.array.itemsize" title="Permalink to this definition">¶</a></dt>
<dd>The length in bytes of one array item in the internal representation.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.append">
array.append(x)<a class="headerlink" href="#array.array.append" title="Permalink to this definition">¶</a></dt>
<dd>Append a new item with value x to the end of the array.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.buffer_info">
array.buffer_info()<a class="headerlink" href="#array.array.buffer_info" title="Permalink to this definition">¶</a></dt>
<dd>Return a tuple <code class="docutils literal notranslate">(address, length)</code> giving the current memory address and the
length in elements of the buffer used to hold array’s contents. The size of the
memory buffer in bytes can be computed as <code class="docutils literal notranslate">array.buffer_info()[1] *
array.itemsize</code>. This is occasionally useful when working with low-level (and
inherently unsafe) I/O interfaces that require memory addresses, such as certain
<code class="xref c c-func docutils literal notranslate">ioctl()</code> operations. The returned numbers are valid as long as the array
exists and no length-changing operations are applied to it.
<div class="admonition note">
Note
When using array objects from code written in C or C++ (the only way to
effectively make use of this information), it makes more sense to use the buffer
interface supported by array objects. This method is maintained for backward
compatibility and should be avoided in new code. The buffer interface is
documented in <a class="reference internal" href="../c-api/buffer.html#bufferobjects">Buffers and Memoryview Objects</a>.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.byteswap">
array.byteswap()<a class="headerlink" href="#array.array.byteswap" title="Permalink to this definition">¶</a></dt>
<dd>“Byteswap” all items of the array. This is only supported for values which are
1, 2, 4, or 8 bytes in size; for other types of values, <code class="xref py py-exc docutils literal notranslate">RuntimeError</code> is
raised. It is useful when reading data from a file written on a machine with a
different byte order.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.count">
array.count(x)<a class="headerlink" href="#array.array.count" title="Permalink to this definition">¶</a></dt>
<dd>Return the number of occurrences of x in the array.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.extend">
array.extend(iterable)<a class="headerlink" href="#array.array.extend" title="Permalink to this definition">¶</a></dt>
<dd>Append items from iterable to the end of the array. If iterable is another
array, it must have exactly the same type code; if not, <code class="xref py py-exc docutils literal notranslate">TypeError</code> will
be raised. If iterable is not an array, it must be iterable and its elements
must be the right type to be appended to the array.
<div class="versionchanged">
Changed in version 2.4: Formerly, the argument could only be another array.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.fromfile">
array.fromfile(f, n)<a class="headerlink" href="#array.array.fromfile" title="Permalink to this definition">¶</a></dt>
<dd>Read n items (as machine values) from the file object f and append them to
the end of the array. If less than n items are available, <code class="xref py py-exc docutils literal notranslate">EOFError</code> is
raised, but the items that were available are still inserted into the array.
f must be a real built-in file object; something else with a <a class="reference internal" href="#array.array.read" title="array.array.read"><code class="xref py py-meth docutils literal notranslate">read()</code></a>
method won’t do.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.fromlist">
array.fromlist(list)<a class="headerlink" href="#array.array.fromlist" title="Permalink to this definition">¶</a></dt>
<dd>Append items from the list. This is equivalent to <code class="docutils literal notranslate">for x in list:
a.append(x)</code> except that if there is a type error, the array is unchanged.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.fromstring">
array.fromstring(s)<a class="headerlink" href="#array.array.fromstring" title="Permalink to this definition">¶</a></dt>
<dd>Appends items from the string, interpreting the string as an array of machine
values (as if it had been read from a file using the <a class="reference internal" href="#array.array.fromfile" title="array.array.fromfile"><code class="xref py py-meth docutils literal notranslate">fromfile()</code></a> method).
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.fromunicode">
array.fromunicode(s)<a class="headerlink" href="#array.array.fromunicode" title="Permalink to this definition">¶</a></dt>
<dd>Extends this array with data from the given unicode string. The array must
be a type <code class="docutils literal notranslate">'u'</code> array; otherwise a <code class="xref py py-exc docutils literal notranslate">ValueError</code> is raised. Use
<code class="docutils literal notranslate">array.fromstring(unicodestring.encode(enc))</code> to append Unicode data to an
array of some other type.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.index">
array.index(x)<a class="headerlink" href="#array.array.index" title="Permalink to this definition">¶</a></dt>
<dd>Return the smallest i such that i is the index of the first occurrence of
x in the array.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.insert">
array.insert(i, x)<a class="headerlink" href="#array.array.insert" title="Permalink to this definition">¶</a></dt>
<dd>Insert a new item with value x in the array before position i. Negative
values are treated as being relative to the end of the array.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.pop">
array.pop([i])<a class="headerlink" href="#array.array.pop" title="Permalink to this definition">¶</a></dt>
<dd>Removes the item with the index i from the array and returns it. The optional
argument defaults to <code class="docutils literal notranslate">-1</code>, so that by default the last item is removed and
returned.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.read">
array.read(f, n)<a class="headerlink" href="#array.array.read" title="Permalink to this definition">¶</a></dt>
<dd><div class="deprecated">
Deprecated since version 1.5.1: Use the <a class="reference internal" href="#array.array.fromfile" title="array.array.fromfile"><code class="xref py py-meth docutils literal notranslate">fromfile()</code></a> method.
</div>
Read n items (as machine values) from the file object f and append them to
the end of the array. If less than n items are available, <code class="xref py py-exc docutils literal notranslate">EOFError</code> is
raised, but the items that were available are still inserted into the array.
f must be a real built-in file object; something else with a <a class="reference internal" href="#array.array.read" title="array.array.read"><code class="xref py py-meth docutils literal notranslate">read()</code></a>
method won’t do.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.remove">
array.remove(x)<a class="headerlink" href="#array.array.remove" title="Permalink to this definition">¶</a></dt>
<dd>Remove the first occurrence of x from the array.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.reverse">
array.reverse()<a class="headerlink" href="#array.array.reverse" title="Permalink to this definition">¶</a></dt>
<dd>Reverse the order of the items in the array.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.tofile">
array.tofile(f)<a class="headerlink" href="#array.array.tofile" title="Permalink to this definition">¶</a></dt>
<dd>Write all items (as machine values) to the file object f.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.tolist">
array.tolist()<a class="headerlink" href="#array.array.tolist" title="Permalink to this definition">¶</a></dt>
<dd>Convert the array to an ordinary list with the same items.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.tostring">
array.tostring()<a class="headerlink" href="#array.array.tostring" title="Permalink to this definition">¶</a></dt>
<dd>Convert the array to an array of machine values and return the string
representation (the same sequence of bytes that would be written to a file by
the <a class="reference internal" href="#array.array.tofile" title="array.array.tofile"><code class="xref py py-meth docutils literal notranslate">tofile()</code></a> method.)
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.tounicode">
array.tounicode()<a class="headerlink" href="#array.array.tounicode" title="Permalink to this definition">¶</a></dt>
<dd>Convert the array to a unicode string. The array must be a type <code class="docutils literal notranslate">'u'</code> array;
otherwise a <code class="xref py py-exc docutils literal notranslate">ValueError</code> is raised. Use <code class="docutils literal notranslate">array.tostring().decode(enc)</code> to
obtain a unicode string from an array of some other type.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="array.array.write">
array.write(f)<a class="headerlink" href="#array.array.write" title="Permalink to this definition">¶</a></dt>
<dd><div class="deprecated">
Deprecated since version 1.5.1: Use the <a class="reference internal" href="#array.array.tofile" title="array.array.tofile"><code class="xref py py-meth docutils literal notranslate">tofile()</code></a> method.
</div>
Write all items (as machine values) to the file object f.
</dd></dl>

When an array object is printed or converted to a string, it is represented as
<code class="docutils literal notranslate">array(typecode, initializer)</code>. The initializer is omitted if the array is
empty, otherwise it is a string if the typecode is <code class="docutils literal notranslate">'c'</code>, otherwise it is a
list of numbers. The string is guaranteed to be able to be converted back to an
array with the same type and value using <a class="reference internal" href="functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate">eval()</code></a>, so long as the
<a class="reference internal" href="#array.array" title="array.array"><code class="xref py py-class docutils literal notranslate">array</code></a> class has been imported using <code class="docutils literal notranslate">from array import array</code>.
Examples:
<div class="highlight-default notranslate"><div class="highlight"><pre>array(&#39;l&#39;)
array(&#39;c&#39;, &#39;hello world&#39;)
array(&#39;u&#39;, u&#39;hello \u2641&#39;)
array(&#39;l&#39;, [1, 2, 3, 4, 5])
array(&#39;d&#39;, [1.0, 2.0, 3.14])
</pre></div>
</div>
<div class="admonition seealso">
See also
<dl class="simple">
<dt>Module <a class="reference internal" href="struct.html#module-struct" title="struct: Interpret strings as packed binary data."><code class="xref py py-mod docutils literal notranslate">struct</code></a></dt><dd>Packing and unpacking of heterogeneous binary data.
</dd>
<dt>Module <a class="reference internal" href="xdrlib.html#module-xdrlib" title="xdrlib: Encoders and decoders for the External Data Representation (XDR)."><code class="xref py py-mod docutils literal notranslate">xdrlib</code></a></dt><dd>Packing and unpacking of External Data Representation (XDR) data as used in some
remote procedure call systems.
</dd>
<dt><a class="reference external" href="https://docs.scipy.org/doc/">The Numerical Python Documentation</a></dt><dd>The Numeric Python extension (NumPy) defines another array type; see
<a class="reference external" href="http://www.numpy.org/">http://www.numpy.org/</a> for further information about Numerical Python.
</dd>
</dl>
</div>
</section>

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