forked from yasoob/intermediatePython
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathfor_-_else.html
More file actions
112 lines (101 loc) · 7.49 KB
/
Copy pathfor_-_else.html
File metadata and controls
112 lines (101 loc) · 7.49 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>For - Else</title>
<link rel="stylesheet" href="_static/epub.css" type="text/css" />
<link rel="stylesheet" href="_static/pygments.css" type="text/css" />
</head>
<body role="document">
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="open_function.html" title="Open function"
accesskey="N">next</a></li>
<li class="right" >
<a href="one_liners.html" title="One Liners"
accesskey="P">previous</a> |</li>
<li class="nav-item nav-item-0"><a href="index.html">Python Tips 0.1 documentation</a> »</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="body" role="main">
<div class="section" id="for-else">
<h1>For - Else</h1>
<p>Loops are an integral part of any language. Likewise <code class="docutils literal"><span class="pre">for</span></code> loops are
an important part of Python. However there are a few things which most
beginners do not know about them. We will discuss a few of them one by
one.</p>
<p>Let’s first start of by what we know. We know that we can use for loops
like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">fruits</span> <span class="o">=</span> <span class="p">[</span><span class="s">'apple'</span><span class="p">,</span> <span class="s">'banana'</span><span class="p">,</span> <span class="s">'mango'</span><span class="p">]</span>
<span class="k">for</span> <span class="n">fruit</span> <span class="ow">in</span> <span class="n">fruits</span><span class="p">:</span>
<span class="k">print</span> <span class="n">fruit</span><span class="o">.</span><span class="n">capitalize</span><span class="p">()</span>
<span class="c"># Output: Apple</span>
<span class="c"># Banana</span>
<span class="c"># Mango</span>
</pre></div>
</div>
<p>That is the very basic structure of a for loop. Now let’s move on to
some of the lesser known features of <code class="docutils literal"><span class="pre">for</span></code> loops in Python.</p>
<div class="section" id="else-clause">
<h2>1.<code class="docutils literal"><span class="pre">else</span></code> clause:</h2>
<p>For loops also have an <code class="docutils literal"><span class="pre">else</span></code> clause which most of us are unfamiliar
with. The <code class="docutils literal"><span class="pre">else</span></code> clause executes when the loop completes normally.
This means that the loop did not encounter any <code class="docutils literal"><span class="pre">break</span></code>. They are
really useful once you understand where to use them. I myself came to
know about them a lot later.</p>
<p>The common construct is to run a loop and search for an item. If the
item is found, we break the loop using <code class="docutils literal"><span class="pre">break</span></code>. There are two
scenarios in which the loop may end. The first one is when the item is
found and <code class="docutils literal"><span class="pre">break</span></code> is encountered. The second scenario is that the loop
ends. Now we may want to know which one of these is the reason for a
loops completion. One method is to set a flag and then check it once the
loop ends. Another is to use the <code class="docutils literal"><span class="pre">else</span></code> clause.</p>
<p>This is the basic structure of a <code class="docutils literal"><span class="pre">for/else</span></code> loop:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="k">for</span> <span class="n">item</span> <span class="ow">in</span> <span class="n">container</span><span class="p">:</span>
<span class="k">if</span> <span class="n">search_comething</span><span class="p">(</span><span class="n">item</span><span class="p">):</span>
<span class="c"># Found it!</span>
<span class="n">process</span><span class="p">(</span><span class="n">item</span><span class="p">)</span>
<span class="k">break</span>
<span class="k">else</span><span class="p">:</span>
<span class="c"># Didn't find anything..</span>
<span class="n">not_found_in_container</span><span class="p">()</span>
</pre></div>
</div>
<p>Consider this simple example which I took from the official
documentation:</p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">10</span><span class="p">):</span>
<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="n">n</span><span class="p">):</span>
<span class="k">if</span> <span class="n">n</span> <span class="o">%</span> <span class="n">x</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="k">print</span> <span class="n">n</span><span class="p">,</span> <span class="s">'equals'</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="s">'*'</span><span class="p">,</span> <span class="n">n</span><span class="o">/</span><span class="n">x</span>
<span class="k">break</span>
</pre></div>
</div>
<p>It outputs the prime numbers between 2 to 10. Now for the fun part. We
can add an additional <code class="docutils literal"><span class="pre">else</span></code> block which catches the numbers which are
not prime and tells us so:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">10</span><span class="p">):</span>
<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="n">n</span><span class="p">):</span>
<span class="k">if</span> <span class="n">n</span> <span class="o">%</span> <span class="n">x</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
<span class="k">print</span> <span class="n">n</span><span class="p">,</span> <span class="s">'equals'</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="s">'*'</span><span class="p">,</span> <span class="n">n</span><span class="o">/</span><span class="n">x</span>
<span class="k">break</span>
<span class="k">else</span><span class="p">:</span>
<span class="c"># loop fell through without finding a factor</span>
<span class="k">print</span> <span class="n">n</span><span class="p">,</span> <span class="s">'is a prime number'</span>
</pre></div>
</div>
</div>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="footer" role="contentinfo">
© Copyright 2015, Muhammad Yasoob Ullah Khalid.
</div>
</body>
</html>