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-<head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Chapter. strings_dicts</title><link rel="stylesheet" href="/review/support/styles.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.74.3" /><link rel="shortcut icon" type="image/png" href="/review/support/figs/favicon.png" /><script type="text/javascript" src="/review/support/jquery-min.js"></script><script type="text/javascript" src="/review/support/form.js"></script><script type="text/javascript" src="/review/support/hsbook.js"></script></head>
-<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="#id2983086">Strings</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="#id2981673">1. String Formatting</a></span></dt>
-<dt><span class="section"><a href="#id3034090">2. String Methods</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="#id3034105">2.1. <span class="strong"><strong>find</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034135">2.2. <span class="strong"><strong>join</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034175">2.3. <span class="strong"><strong>lower</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034206">2.4. <span class="strong"><strong>replace</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034262">2.5. <span class="strong"><strong>split</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034321">2.6. <span class="strong"><strong>strip</strong></span></a></span></dt>
-</dl></dd>
-<dt><span class="section"><a href="#id3034366">3. Introduction to the standard library</a></span></dt>
-<dt><span class="section"><a href="#id3034442">4. I/O: Reading and Writing Files</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="#id3034472">4.1. Opening Files</a></span></dt>
-<dt><span class="section"><a href="#id3034646">4.2. Reading and Writing files</a></span></dt>
-</dl></dd>
-<dt><span class="section"><a href="#id3034811">5. Dictionaries</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="#id3034868">5.1. <span class="strong"><strong>dict()</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034932">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="id2983086"></a>Strings</h2></div></div>
-<hr />
-</div>
-<div class="toc">
-<p><b>Table of Contents</b></p>
-<dl>
-<dt><span class="section"><a href="#id2981673">1. String Formatting</a></span></dt>
-<dt><span class="section"><a href="#id3034090">2. String Methods</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="#id3034105">2.1. <span class="strong"><strong>find</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034135">2.2. <span class="strong"><strong>join</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034175">2.3. <span class="strong"><strong>lower</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034206">2.4. <span class="strong"><strong>replace</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034262">2.5. <span class="strong"><strong>split</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034321">2.6. <span class="strong"><strong>strip</strong></span></a></span></dt>
-</dl></dd>
-<dt><span class="section"><a href="#id3034366">3. Introduction to the standard library</a></span></dt>
-<dt><span class="section"><a href="#id3034442">4. I/O: Reading and Writing Files</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="#id3034472">4.1. Opening Files</a></span></dt>
-<dt><span class="section"><a href="#id3034646">4.2. Reading and Writing files</a></span></dt>
-</dl></dd>
-<dt><span class="section"><a href="#id3034811">5. Dictionaries</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="#id3034868">5.1. <span class="strong"><strong>dict()</strong></span></a></span></dt>
-<dt><span class="section"><a href="#id3034932">5.2. Dictionary Methods</a></span></dt>
-</dl></dd>
-</dl>
-</div>
-<p id="ch4strings_dicts_1">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">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="id2981673"></a>1.String Formatting</h2></div></div></div>
-<p id="ch4strings_dicts_3">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">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">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">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="id3034090"></a>2.String Methods</h2></div></div></div>
-<p id="ch4strings_dicts_7">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="id3034105"></a>2.1.<span class="strong"><strong>find</strong></span>
-</h3></div></div></div>
-<p id="ch4strings_dicts_8">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="id3034135"></a>2.2.<span class="strong"><strong>join</strong></span>
-</h3></div></div></div>
-<p id="ch4strings_dicts_9">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"><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="id3034175"></a>2.3.<span class="strong"><strong>lower</strong></span>
-</h3></div></div></div>
-<p id="ch4strings_dicts_b">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="id3034206"></a>2.4.<span class="strong"><strong>replace</strong></span>
-</h3></div></div></div>
-<p id="ch4strings_dicts_c">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">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="id3034262"></a>2.5.<span class="strong"><strong>split</strong></span>
-</h3></div></div></div>
-<p id="ch4strings_dicts_e">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">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="id3034321"></a>2.6.<span class="strong"><strong>strip</strong></span>
-</h3></div></div></div>
-<p id="ch4strings_dicts_10">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">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="id3034366"></a>3.Introduction to the standard library</h2></div></div></div>
-<p id="ch4strings_dicts_12">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>
-<div class="itemizedlist"><ul class="itemizedlist" type="*">
-<li class="listitem" style="list-style-type: *"><p id="ch4strings_dicts_13"><span class="strong"><strong>abs()</strong></span></p></li>
-<li class="listitem" style="list-style-type: *"><p id="ch4strings_dicts_14"><span class="strong"><strong>dict()</strong></span></p></li>
-<li class="listitem" style="list-style-type: *"><p id="ch4strings_dicts_15"><span class="strong"><strong>enumerate()</strong></span></p></li>
-</ul></div>
-<p id="ch4strings_dicts_16">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="id3034442"></a>4.I/O: Reading and Writing Files</h2></div></div></div>
-<p id="ch4strings_dicts_17">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="id3034472"></a>4.1.Opening Files</h3></div></div></div>
-<p id="ch4strings_dicts_18">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"><span class="emphasis"><em>f = open( filename, mode, buffering)</em></span></p>
-<p id="ch4strings_dicts_1a">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">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"><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">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">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="id3034646"></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="id3034655"></a>4.2.1.<span class="strong"><strong>write()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_1f"><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="id3034694"></a>4.2.2.<span class="strong"><strong>read()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_20"><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">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="id3034729"></a>4.2.3.<span class="strong"><strong>readline()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_22"><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">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="id3034788"></a>4.2.4.<span class="strong"><strong>close()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_24">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="id3034811"></a>5.Dictionaries</h2></div></div></div>
-<p id="ch4strings_dicts_25">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">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="id3034868"></a>5.1.<span class="strong"><strong>dict()</strong></span>
-</h3></div></div></div>
-<p id="ch4strings_dicts_27">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"><span class="strong"><strong>String Formatting with Dictionaries:</strong></span></p>
-<p id="ch4strings_dicts_29">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="id3034932"></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="id3034940"></a>5.2.1.<span class="strong"><strong>clear()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_2a">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="id3034976"></a>5.2.2.<span class="strong"><strong>copy()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_2b">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="id3035006"></a>5.2.3.<span class="strong"><strong>get()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_2c"><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="id3035044"></a>5.2.4.<span class="strong"><strong>has_key()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_2d">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="id3035074"></a>5.2.5.<span class="strong"><strong>pop()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_2e">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="id3035108"></a>5.2.6.<span class="strong"><strong>popitem()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_2f">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="id3035144"></a>5.2.7.<span class="strong"><strong>update()</strong></span>
-</h4></div></div></div>
-<p id="ch4strings_dicts_30">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>
-