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<h1>Efficient arrays of numeric values</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 border="1">
<tr><th>Type code</th>
<th>C Type</th>
<th>Python Type</th>
<th>Minimum size in bytes</th>
<th>Notes</th>
</tr>
<tr><td>'b'</td>
<td>signed char</td>
<td>int</td>
<td>1</td>
<td> </td>
</tr>
<tr><td>'B'</td>
<td>unsigned char</td>
<td>int</td>
<td>1</td>
<td> </td>
</tr>
<tr><td>'u'</td>
<td>Py_UNICODE</td>
<td>Unicode character</td>
<td>2</td>
<td>(1)</td>
</tr>
<tr><td>'h'</td>
<td>signed short</td>
<td>int</td>
<td>2</td>
<td> </td>
</tr>
<tr><td>'H'</td>
<td>unsigned short</td>
<td>int</td>
<td>2</td>
<td> </td>
</tr>
<tr><td>'i'</td>
<td>signed int</td>
<td>int</td>
<td>2</td>
<td> </td>
</tr>
<tr><td>'I'</td>
<td>unsigned int</td>
<td>int</td>
<td>2</td>
<td> </td>
</tr>
<tr><td>'l'</td>
<td>signed long</td>
<td>int</td>
<td>4</td>
<td> </td>
</tr>
<tr><td>'L'</td>
<td>unsigned long</td>
<td>int</td>
<td>4</td>
<td> </td>
</tr>
<tr><td>'q'</td>
<td>signed long long</td>
<td>int</td>
<td>8</td>
<td>(2)</td>
</tr>
<tr><td>'Q'</td>
<td>unsigned long long</td>
<td>int</td>
<td>8</td>
<td>(2)</td>
</tr>
<tr><td>'f'</td>
<td>float</td>
<td>float</td>
<td>4</td>
<td> </td>
</tr>
<tr><td>'d'</td>
<td>double</td>
<td>float</td>
<td>8</td>
<td> </td>
</tr>
</table>
Notes:
<ol>
<li>The 'u' type code corresponds to Python’s obsolete unicode character
Py_UNICODE which is wchar_t. Depending on the platform, it can be 16 bits or 32 bits.
'u' will be removed together with the rest of the Py_UNICODE API.
Deprecated since version 3.3, will be removed in version 4.0.
</li>
<li>The 'q' and 'Q' type codes are available only if the platform C compiler used to build Python supports C long long, or, on Windows, __int64.
New in version 3.3.
</li>
</ol>
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 itemsize attribute.
The module defines the following type:
<dl>
class array.array(typecode[, initializer])
A new array whose items are restricted by typecode, and initialized
from the optional initializer value, which must be a list, a
bytes-like object, or iterable over elements of the
appropriate type.
If given a list or string, the initializer is passed to the new array’s
fromlist(), frombytes(), or fromunicode() method (see below)
to add initial items to the array. Otherwise, the iterable initializer is
passed to the extend() method.
</dl>

<dl>
array.typecodes
A string with all available type codes.
</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,
TypeError is raised. Array objects also implement the buffer interface,
and may be used wherever bytes-like objects are supported.
The following data items and methods are also supported:
<dl>
array.typecode
The typecode character used to create the array.
</dl>

<dl>
array.itemsize
The length in bytes of one array item in the internal representation.
</dl>

<dl>
array.append(x)
Append a new item with value x to the end of the array.
</dl>

<dl>
array.buffer_info()
Return a tuple (address, length) 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 array.buffer_info()[1] * array.itemsize. This is occasionally useful when working with low-level (and inherently unsafe) I/O interfaces that require memory addresses, such as certain ioctl() operations. The returned numbers are valid as long as the array
exists and no length-changing operations are applied to it.

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 Buffer Protocol.
</dl>

<dl>
array.byteswap()
“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, RuntimeError is
raised. It is useful when reading data from a file written on a machine with a
different byte order.
</dl>

<dl>
array.count(x)
Return the number of occurrences of x in the array.
</dl>

<dl>
array.extend(iterable)
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, TypeError 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.
</dl>

<dl>
array.frombytes(s)
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 fromfile() method).

New in version 3.2: fromstring() is renamed to frombytes() for clarity.
</dl>

<dl class="method">
<dt id="array.array.fromfile">
<tt class="descclassname">array.</tt><tt class="descname">fromfile</tt><big>(</big>f, n<big>)</big><a class="headerlink" href="#array.array.fromfile" title="Permalink to this definition">¶</a></dt>
<dd>Read n items (as machine values) from the <a class="reference internal" href="../glossary.html#term-file-object">file object</a> f and append
them to the end of the array. If less than n items are available,
<a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><tt class="xref py py-exc docutils literal">EOFError</tt></a> 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 <tt class="xref py py-meth docutils literal">read()</tt> method won’t do.
</dd></dl>

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

<dl class="method">
<dt id="array.array.fromstring">
<tt class="descclassname">array.</tt><tt class="descname">fromstring</tt><big>(</big><big>)</big><a class="headerlink" href="#array.array.fromstring" title="Permalink to this definition">¶</a></dt>
<dd>Deprecated alias for <a class="reference internal" href="#array.array.frombytes" title="array.array.frombytes"><tt class="xref py py-meth docutils literal">frombytes()</tt></a>.
</dd></dl>

<dl class="method">
<dt id="array.array.fromunicode">
<tt class="descclassname">array.</tt><tt class="descname">fromunicode</tt><big>(</big>s<big>)</big><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 <tt class="docutils literal">'u'</tt> array; otherwise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><tt class="xref py py-exc docutils literal">ValueError</tt></a> is raised. Use
<tt class="docutils literal">array.frombytes(unicodestring.encode(enc))</tt> to append Unicode data to an
array of some other type.
</dd></dl>

<dl class="method">
<dt id="array.array.index">
<tt class="descclassname">array.</tt><tt class="descname">index</tt><big>(</big>x<big>)</big><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="method">
<dt id="array.array.insert">
<tt class="descclassname">array.</tt><tt class="descname">insert</tt><big>(</big>i, x<big>)</big><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="method">
<dt id="array.array.pop">
<tt class="descclassname">array.</tt><tt class="descname">pop</tt><big>(</big>[i]<big>)</big><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 <tt class="docutils literal">-1</tt>, so that by default the last item is removed and
returned.
</dd></dl>

<dl class="method">
<dt id="array.array.remove">
<tt class="descclassname">array.</tt><tt class="descname">remove</tt><big>(</big>x<big>)</big><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="method">
<dt id="array.array.reverse">
<tt class="descclassname">array.</tt><tt class="descname">reverse</tt><big>(</big><big>)</big><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="method">
<dt id="array.array.tobytes">
<tt class="descclassname">array.</tt><tt class="descname">tobytes</tt><big>(</big><big>)</big><a class="headerlink" href="#array.array.tobytes" title="Permalink to this definition">¶</a></dt>
<dd>Convert the array to an array of machine values and return the bytes
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"><tt class="xref py py-meth docutils literal">tofile()</tt></a> method.)
<div class="versionadded">
New in version 3.2: <a class="reference internal" href="#array.array.tostring" title="array.array.tostring"><tt class="xref py py-meth docutils literal">tostring()</tt></a> is renamed to <a class="reference internal" href="#array.array.tobytes" title="array.array.tobytes"><tt class="xref py py-meth docutils literal">tobytes()</tt></a> for clarity.
</div>
</dd></dl>

<dl class="method">
<dt id="array.array.tofile">
<tt class="descclassname">array.</tt><tt class="descname">tofile</tt><big>(</big>f<big>)</big><a class="headerlink" href="#array.array.tofile" title="Permalink to this definition">¶</a></dt>
<dd>Write all items (as machine values) to the <a class="reference internal" href="../glossary.html#term-file-object">file object</a> f.
</dd></dl>

<dl class="method">
<dt id="array.array.tolist">
<tt class="descclassname">array.</tt><tt class="descname">tolist</tt><big>(</big><big>)</big><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="method">
<dt id="array.array.tostring">
<tt class="descclassname">array.</tt><tt class="descname">tostring</tt><big>(</big><big>)</big><a class="headerlink" href="#array.array.tostring" title="Permalink to this definition">¶</a></dt>
<dd>Deprecated alias for <a class="reference internal" href="#array.array.tobytes" title="array.array.tobytes"><tt class="xref py py-meth docutils literal">tobytes()</tt></a>.
</dd></dl>

<dl class="method">
<dt id="array.array.tounicode">
<tt class="descclassname">array.</tt><tt class="descname">tounicode</tt><big>(</big><big>)</big><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 <tt class="docutils literal">'u'</tt> array;
otherwise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><tt class="xref py py-exc docutils literal">ValueError</tt></a> is raised. Use <tt class="docutils literal">array.tobytes().decode(enc)</tt> to
obtain a unicode string from an array of some other type.
</dd></dl>

When an array object is printed or converted to a string, it is represented as
<tt class="docutils literal">array(typecode, initializer)</tt>. The initializer is omitted if the array is
empty, otherwise it is a string if the typecode is <tt class="docutils literal">'u'</tt>, 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"><tt class="xref py py-func docutils literal">eval()</tt></a>, so long as the
<a class="reference internal" href="#module-array" title="array: Space efficient arrays of uniformly typed numeric values."><tt class="xref py py-func docutils literal">array()</tt></a> function has been imported using <tt class="docutils literal">from array import array</tt>.
Examples:
<div class="highlight-python3"><div class="highlight"><pre>array('l')
array('u', 'hello \u2641')
array('l', [1, 2, 3, 4, 5])
array('d', [1.0, 2.0, 3.14])
</pre></div>
</div>
<div class="admonition seealso">
See also
<dl class="last docutils">
<dt>Module <a class="reference internal" href="struct.html#module-struct" title="struct: Interpret bytes as packed binary data."><tt class="xref py py-mod docutils literal">struct</tt></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)."><tt class="xref py py-mod docutils literal">xdrlib</tt></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="http://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>

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Rrc en 15:24 28 nov 2014