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+<title>Chapter 4. strings_dicts</title>
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" id="ch4strings_dicts">
+<div class="titlepage"></div>
+<div class="toc">
+<p><b>Table of Contents</b></p>
+<dl>
+<dt><span class="article"><a href="#id2983496">Strings</a></span></dt>
+<dd><dl>
+<dt><span class="section"><a href="#id2982083">1. String Formatting</a></span></dt>
+<dt><span class="section"><a href="#id3034500">2. String Methods</a></span></dt>
+<dd><dl>
+<dt><span class="section"><a href="#id3034515">2.1. <span class="strong"><strong>find</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034545">2.2. <span class="strong"><strong>join</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034585">2.3. <span class="strong"><strong>lower</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034615">2.4. <span class="strong"><strong>replace</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034672">2.5. <span class="strong"><strong>split</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034731">2.6. <span class="strong"><strong>strip</strong></span></a></span></dt>
+</dl></dd>
+<dt><span class="section"><a href="#id3034775">3. Introduction to the standard library</a></span></dt>
+<dt><span class="section"><a href="#id3034853">4. I/O: Reading and Writing Files</a></span></dt>
+<dd><dl>
+<dt><span class="section"><a href="#id3034883">4.1. Opening Files</a></span></dt>
+<dt><span class="section"><a href="#id3035057">4.2. Reading and Writing files</a></span></dt>
+</dl></dd>
+<dt><span class="section"><a href="#id3035222">5. Dictionaries</a></span></dt>
+<dd><dl>
+<dt><span class="section"><a href="#id3035278">5.1. <span class="strong"><strong>dict()</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3035342">5.2. Dictionary Methods</a></span></dt>
+</dl></dd>
+</dl></dd>
+</dl>
+</div>
+<div class="article" title="Strings">
+<div class="titlepage">
+<div><div><h2 class="title">
+<a name="id2983496"></a>Strings</h2></div></div>
+<hr>
+</div>
+<div class="toc">
+<p><b>Table of Contents</b></p>
+<dl>
+<dt><span class="section"><a href="#id2982083">1. String Formatting</a></span></dt>
+<dt><span class="section"><a href="#id3034500">2. String Methods</a></span></dt>
+<dd><dl>
+<dt><span class="section"><a href="#id3034515">2.1. <span class="strong"><strong>find</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034545">2.2. <span class="strong"><strong>join</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034585">2.3. <span class="strong"><strong>lower</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034615">2.4. <span class="strong"><strong>replace</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034672">2.5. <span class="strong"><strong>split</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3034731">2.6. <span class="strong"><strong>strip</strong></span></a></span></dt>
+</dl></dd>
+<dt><span class="section"><a href="#id3034775">3. Introduction to the standard library</a></span></dt>
+<dt><span class="section"><a href="#id3034853">4. I/O: Reading and Writing Files</a></span></dt>
+<dd><dl>
+<dt><span class="section"><a href="#id3034883">4.1. Opening Files</a></span></dt>
+<dt><span class="section"><a href="#id3035057">4.2. Reading and Writing files</a></span></dt>
+</dl></dd>
+<dt><span class="section"><a href="#id3035222">5. Dictionaries</a></span></dt>
+<dd><dl>
+<dt><span class="section"><a href="#id3035278">5.1. <span class="strong"><strong>dict()</strong></span></a></span></dt>
+<dt><span class="section"><a href="#id3035342">5.2. Dictionary Methods</a></span></dt>
+</dl></dd>
+</dl>
+</div>
+<p id="ch4strings_dicts_1"></a>Strings were briefly introduced previously in the introduction document. In this
+section strings will be presented in greater detail. All the standard operations
+that can be performed on sequences such as indexing, slicing, multiplication, length
+minimum and maximum can be performed on string variables as well. One thing to
+be noted is that strings are immutable, which means that string variables are
+unchangeable. Hence, all item and slice assignments on strings are illegal.
+Let us look at a few example.</p>
+<pre class="programlisting"> >>> name = 'PythonFreak'
+>>> print name[3]
+h
+>>> print name[-1]
+k
+>>> print name[6:]
+Freak
+>>> name[6:0] = 'Maniac'
+Traceback (most recent call last):
+ File "<stdin>", line 1, in <module>
+TypeError: 'str' object does not support item assignment</pre>
+<p id="ch4strings_dicts_2"></a>This is quite expected, since string objects are immutable as already mentioned.
+The error message is clear in mentioning that 'str' object does not support item
+assignment.</p>
+<div class="section" title="1. String Formatting">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="id2982083"></a>1. String Formatting</h2></div></div></div>
+<p id="ch4strings_dicts_3"></a>String formatting can be performed using the string formatting operator represented
+as the percent (%) sign. The string placed before the % sign is formatted with
+the value placed to the right of it. Let us look at a simple example.</p>
+<pre class="programlisting"> >>> format = 'Hello %s, from PythonFreak'
+>>> str1 = 'world!'
+>>> print format % str1
+Hello world!, from PythonFreak</pre>
+<p id="ch4strings_dicts_4"></a>The %s parts of the format string are called the coversion specifiers. The coversion
+specifiers mark the places where the formatting has to be performed in a string.
+In the example the %s is replaced by the value of str1. More than one value can
+also be formatted at a time by specifying the values to be formatted using tuples
+and dictionaries (explained in later sections). Let us look at an example.</p>
+<pre class="programlisting"> >>> format = 'Hello %s, from %s'
+>>> values = ('world!', 'PythonFreak')
+>>> print format % values
+Hello world!, from PythonFreak</pre>
+<p id="ch4strings_dicts_5"></a>In this example it can be observed that the format string contains two conversion
+specifiers and they are formatted using the tuple of values as shown.</p>
+<p id="ch4strings_dicts_6"></a>The s in %s specifies that the value to be replaced is of type string. Values of
+other types can be specified as well such as integers and floats. Integers are
+specified as %d and floats as %f. The precision with which the integer or the
+float values are to be represented can also be specified using a <span class="strong"><strong>.</strong></span> (<span class="strong"><strong>dot</strong></span>)
+followed by the precision value.</p>
+</div>
+<div class="section" title="2. String Methods">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="id3034500"></a>2. String Methods</h2></div></div></div>
+<p id="ch4strings_dicts_7"></a>Similar to list methods, strings also have a rich set of methods to perform various
+operations on strings. Some of the most important and popular ones are presented
+in this section.</p>
+<div class="section" title="2.1. find">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3034515"></a>2.1. <span class="strong"><strong>find</strong></span>
+</h3></div></div></div>
+<p id="ch4strings_dicts_8"></a>The <span class="strong"><strong>find</strong></span> method is used to search for a substring within a given string. It
+returns the left most index of the first occurence of the substring. If the
+substring is not found in the string then it returns -1. Let us look at a few
+examples.</p>
+<pre class="programlisting"> >>> longstring = 'Hello world!, from PythonFreak'
+>>> longstring.find('Python')
+19
+>>> longstring.find('Perl')
+-1</pre>
+</div>
+<div class="section" title="2.2. join">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3034545"></a>2.2. <span class="strong"><strong>join</strong></span>
+</h3></div></div></div>
+<p id="ch4strings_dicts_9"></a>The <span class="strong"><strong>join</strong></span> method is used to join the elements of a sequence. The sequence
+elements that are to be join ed should all be strings. Let us look at a few
+examples.</p>
+<pre class="programlisting"> >>> seq = ['With', 'great', 'power', 'comes', 'great', 'responsibility']
+>>> sep = ' '
+>>> sep.join(seq)
+'With great power comes great responsibility'
+>>> sep = ',!'
+>>> sep.join(seq)
+'With,!great,!power,!comes,!great,!responsibility'</pre>
+<p id="ch4strings_dicts_a"></a><span class="emphasis"><em>Try this yourself</em></span></p>
+<pre class="programlisting"> >>> seq = [12,34,56,78]
+>>> sep.join(seq)</pre>
+</div>
+<div class="section" title="2.3. lower">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3034585"></a>2.3. <span class="strong"><strong>lower</strong></span>
+</h3></div></div></div>
+<p id="ch4strings_dicts_b"></a>The <span class="strong"><strong>lower</strong></span> method, as the name indicates, converts the entire text of a string
+to lower case. It is specially useful in cases where the programmers deal with case
+insensitive data. Let us look at a few examples.</p>
+<pre class="programlisting"> >>> sometext = 'Hello world!, from PythonFreak'
+>>> sometext.lower()
+'hello world!, from pythonfreak'</pre>
+</div>
+<div class="section" title="2.4. replace">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3034615"></a>2.4. <span class="strong"><strong>replace</strong></span>
+</h3></div></div></div>
+<p id="ch4strings_dicts_c"></a>The <span class="strong"><strong>replace</strong></span> method replaces a substring with another substring within
+a given string and returns the new string. Let us look at an example.</p>
+<pre class="programlisting"> >>> sometext = 'Concise, precise and criticise is some of the words that end with ise'
+>>> sometext.replace('is', 'are')
+'Concaree, precaree and criticaree are some of the words that end with aree'</pre>
+<p id="ch4strings_dicts_d"></a>Observe here that all the occurences of the substring <span class="emphasis"><em>is</em></span> have been replaced,
+even the <span class="emphasis"><em>is</em></span> in <span class="emphasis"><em>concise</em></span>, <span class="emphasis"><em>precise</em></span> and <span class="emphasis"><em>criticise</em></span> have been replaced.</p>
+</div>
+<div class="section" title="2.5. split">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3034672"></a>2.5. <span class="strong"><strong>split</strong></span>
+</h3></div></div></div>
+<p id="ch4strings_dicts_e"></a>The <span class="strong"><strong>split</strong></span> is one of the very important string methods. split is the opposite of the
+<span class="strong"><strong>join</strong></span> method. It is used to split a string based on the argument passed as the
+delimiter. It returns a list of strings. By default when no argument is passed it
+splits with <span class="emphasis"><em>space</em></span> (' ') as the delimiter. Let us look at an example.</p>
+<pre class="programlisting"> >>> grocerylist = 'butter, cucumber, beer(a grocery item??), wheatbread'
+>>> grocerylist.split(',')
+['butter', ' cucumber', ' beer(a grocery item??)', ' wheatbread']
+>>> grocerylist.split()
+['butter,', 'cucumber,', 'beer(a', 'grocery', 'item??),', 'wheatbread']</pre>
+<p id="ch4strings_dicts_f"></a>Observe here that in the second case when the delimiter argument was not set
+<span class="strong"><strong>split</strong></span> was done with <span class="emphasis"><em>space</em></span> as the delimiter.</p>
+</div>
+<div class="section" title="2.6. strip">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3034731"></a>2.6. <span class="strong"><strong>strip</strong></span>
+</h3></div></div></div>
+<p id="ch4strings_dicts_10"></a>The <span class="strong"><strong>strip</strong></span> method is used to remove or <span class="strong"><strong>strip</strong></span> off any whitespaces that exist
+to the left and right of a string, but not the whitespaces within a string. Let
+us look at an example.</p>
+<pre class="programlisting"> >>> spacedtext = " Where's the text?? "
+>>> spacedtext.strip()
+"Where's the text??"</pre>
+<p id="ch4strings_dicts_11"></a>Observe that the whitespaces between the words have not been removed.</p>
+<pre class="programlisting"> Note: Very important thing to note is that all the methods shown above do not
+ transform the source string. The source string still remains the same.
+ Remember that **strings are immutable**.</pre>
+</div>
+</div>
+<div class="section" title="3. Introduction to the standard library">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="id3034775"></a>3. Introduction to the standard library</h2></div></div></div>
+<p id="ch4strings_dicts_12"></a>Python is often referred to as a "Batteries included!" language, mainly because
+of the Python Standard Library. The Python Standard Library provides an extensive
+set of features some of which are available directly for use while some require to
+import a few <span class="strong"><strong>modules</strong></span>. The Standard Library provides various built-in functions
+like:</p>
+<span style="color: black"><span style="color: black"><span style="color: black"><p id="ch4strings_dicts_13"></a><span class="strong"><strong>abs()</strong></span></p></span><span style="color: black"><p id="ch4strings_dicts_14"></a><span class="strong"><strong>dict()</strong></span></p></span><span style="color: black"><p id="ch4strings_dicts_15"></a><span class="strong"><strong>enumerate()</strong></span></p></span></span></span><p id="ch4strings_dicts_16"></a>The built-in constants like <span class="strong"><strong>True</strong></span> and <span class="strong"><strong>False</strong></span> are provided by the Standard Library.
+More information about the Python Standard Library is available </p>
+<div class="reference">
+<div class="titlepage"><hr></div>http://docs.python.org/library/</div>
+</div>
+<div class="section" title="4. I/O: Reading and Writing Files">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="id3034853"></a>4. I/O: Reading and Writing Files</h2></div></div></div>
+<p id="ch4strings_dicts_17"></a>Files are very important aspects when it comes to computing and programming.
+Up until now the focus has been on small programs that interacted with users
+through <span class="strong"><strong>input()</strong></span> and <span class="strong"><strong>raw_input()</strong></span>. Generally, for computational purposes
+it becomes necessary to handle files, which are usually large in size as well.
+This section focuses on basics of file handling.</p>
+<div class="section" title="4.1. Opening Files">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3034883"></a>4.1. Opening Files</h3></div></div></div>
+<p id="ch4strings_dicts_18"></a>Files can be opened using the <span class="strong"><strong>open()</strong></span> method. <span class="strong"><strong>open()</strong></span> accepts 3 arguments
+out of which 2 are optional. Let us look at the syntax of <span class="strong"><strong>open()</strong></span>:</p>
+<p id="ch4strings_dicts_19"></a><span class="emphasis"><em>f = open( filename, mode, buffering)</em></span></p>
+<p id="ch4strings_dicts_1a"></a>The <span class="emphasis"><em>filename</em></span> is a compulsory argument while the <span class="emphasis"><em>mode</em></span> and <span class="emphasis"><em>buffering</em></span> are
+optional. The <span class="emphasis"><em>filename</em></span> should be a string and it should be the complete path
+to the file to be opened (The path can be absolute or relative). Let us look at
+an example.</p>
+<pre class="programlisting"> >>> f = open ('basic_python/interim_assessment.rst')</pre>
+<p id="ch4strings_dicts_1b"></a>The <span class="emphasis"><em>mode</em></span> argument specifies the mode in which the file has to be opened.
+The following are the valid mode arguments:</p>
+<p id="ch4strings_dicts_1c"></a><span class="strong"><strong>r</strong></span> - Read mode
+<span class="strong"><strong>w</strong></span> - Write mode
+<span class="strong"><strong>a</strong></span> - Append mode
+<span class="strong"><strong>b</strong></span> - Binary mode
+<span class="strong"><strong>+</strong></span> - Read/Write mode</p>
+<p id="ch4strings_dicts_1d"></a>The read mode opens the file as a read-only document. The write mode opens the
+file in the Write only mode. In the write mode, if the file existed prior to the
+opening, the previous contents of the file are erased. The append mode opens the
+file in the write mode but the previous contents of the file are not erased and
+the current data is appended onto the file.
+The binary and the read/write modes are special in the sense that they are added
+onto other modes. The read/write mode opens the file in the reading and writing
+mode combined. The binary mode can be used to open a files that do not contain
+text. Binary files such as images should be opened in the binary mode. Let us look
+at a few examples.</p>
+<pre class="programlisting"> >>> f = open ('basic_python/interim_assessment.rst', 'r')
+>>> f = open ('armstrong.py', 'r+')</pre>
+<p id="ch4strings_dicts_1e"></a>The third argument to the <span class="strong"><strong>open()</strong></span> method is the <span class="emphasis"><em>buffering</em></span> argument. This takes
+a boolean value, <span class="emphasis"><em>True</em></span> or <span class="emphasis"><em>1</em></span> indicates that buffering has to be enabled on the file,
+that is the file is loaded on to the main memory and the changes made to the file are
+not immediately written to the disk. If the <span class="emphasis"><em>buffering</em></span> argument is <span class="emphasis"><em>0</em></span> or <span class="emphasis"><em>False</em></span> the
+changes are directly written on to the disk immediately.</p>
+</div>
+<div class="section" title="4.2. Reading and Writing files">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3035057"></a>4.2. Reading and Writing files</h3></div></div></div>
+<div class="section" title="4.2.1. write()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035066"></a>4.2.1. <span class="strong"><strong>write()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_1f"></a><span class="strong"><strong>write()</strong></span>, evidently, is used to write data onto a file. It takes the data to
+be written as the argument. The data can be a string, an integer, a float or any
+other datatype. In order to be able to write data onto a file, the file has to
+be opened in one of <span class="strong"><strong>w</strong></span>, <span class="strong"><strong>a</strong></span> or <span class="strong"><strong>+</strong></span> modes.</p>
+</div>
+<div class="section" title="4.2.2. read()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035105"></a>4.2.2. <span class="strong"><strong>read()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_20"></a><span class="strong"><strong>read()</strong></span> is used to read data from a file. It takes the number of bytes of data
+to be read as the argument. If nothing is specified by default it reads the entire
+contents from the current position to the end of file.</p>
+<p id="ch4strings_dicts_21"></a>Let us look at a few examples:</p>
+<pre class="programlisting"> >>> f = open ('randomtextfile', 'w')
+>>> f.write('Hello all, this is PythonFreak. This is a random text file.')
+>>> f = open ('../randomtextfile', 'r')
+>>> f = open ('../randomtextfile', 'r')
+>>> f.read(5)
+'Hello'
+>>> f.read()
+' all, this is PythonFreak. This is a random text file.'
+>>> f.close()</pre>
+</div>
+<div class="section" title="4.2.3. readline()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035140"></a>4.2.3. <span class="strong"><strong>readline()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_22"></a><span class="strong"><strong>readline()</strong></span> is used to read a file line by line. <span class="strong"><strong>readline()</strong></span> reads a line
+of a file at a time. When an argument is passed to <span class="strong"><strong>readline()</strong></span> it reads that
+many bytes from the current line.</p>
+<p id="ch4strings_dicts_23"></a>One other method to read a file line by line is using the <span class="strong"><strong>read()</strong></span> and the
+<span class="strong"><strong>for</strong></span> construct. Let us look at this block of code as an example.</p>
+<pre class="programlisting"> >>> f = open('../randomtextfile', 'r')
+>>> for line in f:
+... print line
+...
+Hello all!
+
+This is PythonFreak on the second line.
+
+This is a random text file on line 3</pre>
+</div>
+<div class="section" title="4.2.4. close()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035199"></a>4.2.4. <span class="strong"><strong>close()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_24"></a>One must always close all the files that have been opened. Although, files opened
+will be closed automatically when the program ends. When files opened in read mode
+are not closed it might lead to uselessly locked sometimes. In case of files
+opened in the write mode it is more important to close the files. This is because,
+Python maybe using the file in the buffering mode and when the file is not closed
+the buffer maybe lost completely and the changes made to the file are lost forever.</p>
+</div>
+</div>
+</div>
+<div class="section" title="5. Dictionaries">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="id3035222"></a>5. Dictionaries</h2></div></div></div>
+<p id="ch4strings_dicts_25"></a>A dictionary in general, are designed to be able to look up meanings of words.
+Similarly, the Python dictionaries are also designed to look up for a specific
+key and retrieve the corresponding value. Dictionaries are data structures that
+provide key-value mappings. Dictionaries are similar to lists except that instead
+of the values having integer indexes, dictionaries have keys or strings as indexes.
+Let us look at an example of how to define dictionaries.</p>
+<pre class="programlisting"> >>> dct = { 'Sachin': 'Tendulkar', 'Rahul': 'Dravid', 'Anil': 'Kumble'}</pre>
+<p id="ch4strings_dicts_26"></a>The dictionary consists of pairs of strings, which are called <span class="emphasis"><em>keys</em></span> and their
+corresponding <span class="emphasis"><em>values</em></span> separated by <span class="emphasis"><em>:</em></span> and each of these <span class="emphasis"><em>key-value</em></span> pairs are
+comma(',') separated and the entire structure wrapped in a pair curly braces <span class="emphasis"><em>{}</em></span>.</p>
+<pre class="programlisting"> Note: The data inside a dictionary is not ordered. The order in which you enter
+the key-value pairs is not the order in which they are stored in the dictionary.
+Python has an internal storage mechanism for that which is out of the purview
+of this document.</pre>
+<div class="section" title="5.1. dict()">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3035278"></a>5.1. <span class="strong"><strong>dict()</strong></span>
+</h3></div></div></div>
+<p id="ch4strings_dicts_27"></a>The <span class="strong"><strong>dict()</strong></span> function is used to create dictionaries from other mappings or other
+dictionaries. Let us look at an example.</p>
+<pre class="programlisting"> >>> diction = dict(mat = 133, avg = 52.53)</pre>
+<p id="ch4strings_dicts_28"></a><span class="strong"><strong>String Formatting with Dictionaries:</strong></span></p>
+<p id="ch4strings_dicts_29"></a>String formatting was discussed in the previous section and it was mentioned that
+dictionaries can also be used for formatting more than one value. This section
+focuses on the formatting of strings using dictionaries. String formatting using
+dictionaries is more appealing than doing the same with tuples. Here the <span class="emphasis"><em>keyword</em></span>
+can be used as a place holder and the <span class="emphasis"><em>value</em></span> corresponding to it is replaced in
+the formatted string. Let us look at an example.</p>
+<pre class="programlisting"> >>> player = { 'Name':'Rahul Dravid', 'Matches':133, 'Avg':52.53, '100s':26 }
+>>> strng = '%(Name)s has played %(Matches)d with an average of %(Avg).2f and has %(100s)d hundreds to his name.'
+>>> print strng % player
+Rahul Dravid has played 133 with an average of 52.53 and has 26 hundreds to his name.</pre>
+</div>
+<div class="section" title="5.2. Dictionary Methods">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="id3035342"></a>5.2. Dictionary Methods</h3></div></div></div>
+<div class="section" title="5.2.1. clear()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035351"></a>5.2.1. <span class="strong"><strong>clear()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_2a"></a>The <span class="strong"><strong>clear()</strong></span> method removes all the existing <span class="emphasis"><em>key-value</em></span> pairs from a dictionary.
+It returns <span class="emphasis"><em>None</em></span> or rather does not return anything. It is a method that changes
+the object. It has to be noted here that dictionaries are not immutable. Let us
+look at an example.</p>
+<pre class="programlisting"> >>> dct
+{'Anil': 'Kumble', 'Sachin': 'Tendulkar', 'Rahul': 'Dravid'}
+>>> dct.clear()
+>>> dct
+{}</pre>
+</div>
+<div class="section" title="5.2.2. copy()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035386"></a>5.2.2. <span class="strong"><strong>copy()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_2b"></a>The <span class="strong"><strong>copy()</strong></span> returns a copy of a given dictionary. Let us look at an example.</p>
+<pre class="programlisting"> >>> dct = {'Anil': 'Kumble', 'Sachin': 'Tendulkar', 'Rahul': 'Dravid'}
+>>> dctcopy = dct.copy()
+>>> dctcopy
+{'Anil': 'Kumble', 'Sachin': 'Tendulkar', 'Rahul': 'Dravid'}</pre>
+</div>
+<div class="section" title="5.2.3. get()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035417"></a>5.2.3. <span class="strong"><strong>get()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_2c"></a><span class="strong"><strong>get()</strong></span> returns the <span class="emphasis"><em>value</em></span> for the <span class="emphasis"><em>key</em></span> passed as the argument and if the
+<span class="emphasis"><em>key</em></span> does not exist in the dictionary, it returns <span class="emphasis"><em>None</em></span>. Let us look at an
+example.</p>
+<pre class="programlisting"> >>> print dctcopy.get('Saurav')
+None
+>>> print dctcopy.get('Anil')
+Kumble</pre>
+</div>
+<div class="section" title="5.2.4. has_key()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035455"></a>5.2.4. <span class="strong"><strong>has_key()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_2d"></a>This method returns <span class="emphasis"><em>True</em></span> if the given <span class="emphasis"><em>key</em></span> is in the dictionary, else it returns
+<span class="emphasis"><em>False</em></span>.</p>
+<pre class="programlisting"> >>> dctcopy.has_key('Saurav')
+False
+>>> dctcopy.has_key('Sachin')
+True</pre>
+</div>
+<div class="section" title="5.2.5. pop()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035485"></a>5.2.5. <span class="strong"><strong>pop()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_2e"></a>This method is used to retrieve the <span class="emphasis"><em>value</em></span> of a given <span class="emphasis"><em>key</em></span> and subsequently
+remove the <span class="emphasis"><em>key-value</em></span> pair from the dictionary. Let us look at an example.</p>
+<pre class="programlisting"> >>> print dctcopy.pop('Sachin')
+Tendulkar
+>>> dctcopy
+{'Anil': 'Kumble', 'Rahul': 'Dravid'}</pre>
+</div>
+<div class="section" title="5.2.6. popitem()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035519"></a>5.2.6. <span class="strong"><strong>popitem()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_2f"></a>This method randomly pops a <span class="emphasis"><em>key-value</em></span> pair from a dictionary and returns it.
+The <span class="emphasis"><em>key-value</em></span> pair returned is removed from the dictionary. Let us look at an
+example.</p>
+<pre class="programlisting"> >>> print dctcopy.popitem()
+('Anil', 'Kumble')
+>>> dctcopy
+{'Rahul': 'Dravid'}
+
+Note that the item chosen is completely random since dictionaries are unordered
+as mentioned earlier.</pre>
+</div>
+<div class="section" title="5.2.7. update()">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="id3035555"></a>5.2.7. <span class="strong"><strong>update()</strong></span>
+</h4></div></div></div>
+<p id="ch4strings_dicts_30"></a>The <span class="strong"><strong>update()</strong></span> method updates the contents of one dictionary with the contents
+of another dictionary. For items with existing <span class="emphasis"><em>keys</em></span> their <span class="emphasis"><em>values</em></span> are updated,
+and the rest of the items are added. Let us look at an example.</p>
+<pre class="programlisting"> >>> dctcopy.update(dct)
+>>> dct
+{'Anil': 'Kumble', 'Sachin': 'Tendulkar', 'Rahul': 'Dravid'}
+>>> dctcopy
+{'Anil': 'Kumble', 'Sachin': 'Tendulkar', 'Rahul': 'Dravid'}</pre>
+</div>
+</div>
+</div>
+</div>
+</div></body>
+</html>