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<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Diggernaut: Documentation for Meta-Language | Conditional Flow | Using If</title>
<meta name="description" content="Learning how to build logical branching in the scraper algorithm.">
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<h1>Conditional Flow</h1>
<div>
<h2>Using If</h2>
<p class="flow-text">
When you scraping something, you often end up with situations when some operations should be done depending on certain condition.
To check the condition, you can use the <span class = "hlt2">if</span> command. This command works with strings,
integer and floating-point values. The command compare the value of the register with explicitly given value as parameter,
so command can only be used in a block context.
</p>
<p class="flow-text">
You can use following parameters:
</p>
<table class="responsive-table highlight">
<thead>
<tr>
<th data-field="parameter">Parameter</th>
<th data-field="description">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td class="centered">match|eq|gt|lt|nlt</td>
<td>Modes, which command work with:<br/>
<span class="hlt">match</span> - checks whether the value of the register contains the passed parameter;<br/>
<span class="hlt">eq</span> - checks whether the passed value is equal to the value in the register;<br/>
<span class="hlt">gt</span> - checks whether the value of the register is greater than the passed parameter;<br/>
<span class="hlt">lt</span> - checks whether the value of the register is less than the passed parameter;<br/>
<span class="hlt">nlt</span> - checks whether the value of the register is not less than the passed parameter.
</td>
</tr>
<tr>
<td>type</td>
<td>Values type for comparison:<br/>
<span class="hlt">string</span> - for string values comparison;<br/>
<span class="hlt">int</span> - for integer values comparison;<br/>
<span class="hlt">float</span> - for float values comparison.<br/>
If not passed, default <span class="hlt">string</span> type is used.
</td>
</tr>
<tr>
<td>do</td>
<td>A block of commands to execute if the condition is met. Optional parameter.</td>
</tr>
<tr>
<td>else</td>
<td>A block of commands to execute if the condition is not met. Optional parameter.</td>
</tr>
</tbody>
</table>
<p class="flow-text">
Examples of <span class="hlt2">if</span> notation:
</p>
<pre class="language-yaml">
<code class="language-yaml"># COMPARISON USING REGULAR EXPRESSION
- if:
match: regex
# IF MATCHED REGEX - BLOCK `do` WILL BE EXECUTED
do:
..
..
# IF NOT - BLOCK `else` WILL BE EXECUTED
else:
..
..
</code></pre>
<pre class="language-yaml">
<code class="language-yaml"># COMPARISON USING REGULAR EXPRESSION
# BUT ONLY `do` USED, WITHOUT `else` LOGIC BLOCK
# WORKS SAME WAY IN OTHER MODES
- if:
match: regex
# IF MATCHED REGEX - BLOCK `do` WILL BE EXECUTED
do:
..
..
</code></pre>
<pre class="language-yaml">
<code class="language-yaml"># COMPARISON USING REGULAR EXPRESSION
# BUT ONLY `else` USED
# WORKS SAME WAY IN OTHER MODES
- if:
match: regex
# IF NOT MATCHED - BLOCK `else` WILL BE EXECUTED
else:
..
..
</code></pre>
<pre class="language-yaml">
<code class="language-yaml"># COMPARISON OF INTEGER VALUES
- if:
eq: 0
type: int
# IF TRUE - BLOCK `do` WILL BE EXECUTED
do:
..
..
# IF FALSE - BLOCK `else` WILL BE EXECUTED
else:
..
..
</code></pre>
<pre class="language-yaml">
<code class="language-yaml"># COMPARISON OF INTEGER VALUES
- if:
gt: 0
type: int
# IF REGISTER VALUE IS GREATER THAN 0, BLOCK `do` WILL BE EXECUTED
do:
..
..
# IN OTHER CASE - BLOCK `else` WILL BE EXECUTED
else:
..
..
- if:
lt: 0
type: int
# IF REGISTER VALUE IS LESS THAN 0, BLOCK `do` WILL BE EXECUTED
do:
..
..
# IN OTHER CASE - BLOCK `else` WILL BE EXECUTED
else:
..
..
- if:
nlt: 0
type: int
# IF REGISTER VALUE IS NOT LESS THAN 0, BLOCK `do` WILL BE EXECUTED
do:
..
..
# IN OTHER CASE - BLOCK `else` WILL BE EXECUTED
else:
..
..
</code></pre>
<span class="spacer"></span>
<p class="flow-text">
Let's overview different cases of using <span class="hlt2">if</span> command, and use following HTML source for it:
</p>
<pre class="language-markup">
<code class="language-markup"><ul class="list">
<li class="list-item" id="1">Some text</li>
<li class="list-item" id="item=2"><a href="http://somesite.com/">Link</a></li>
<li class="list-item" id="item=3">Some other text</li>
</ul>
</code></pre>
<p class="flow-text">
Example of <span class="hlt">match</span> mode usage:
</p>
<div class="row">
<div class="col s12">
<ul class="tabs excdark">
<li class="tab col s4"><a class="active" href="#if_1">If</a></li>
<li class="tab col s4"><a href="#if_2">else</a></li>
<li class="tab col s4"><a href="#if_3">if/else</a></li>
</ul>
</div>
<div id="if_1" class="col s12">
<pre class="language-yaml">
<code class="language-yaml"># FIND ALL `li`
- find:
path: li
do:
- parse
# CHECK IF THERE IS WORD `text` IN THE REGISTER
- if:
match: text
do:
# IF TRUE, SET OBJECT FIELD WITH THE VALUE OF THE REGISTER
- object_field_set:
object: someobj
field: somefield
</code></pre>
</div>
<div id="if_2" class="col s12">
<pre class="language-yaml">
<code class="language-yaml"># FIND ALL `li`
- find:
path: li
do:
- parse
# CHECK IF THERE IS WORD `text` IN THE REGISTER
- if:
match: text
# IF NOT FOUND, FIND `a`
else:
- find:
path: a
do:
# PARSE ATTRIBUTE `href` TO THE REGISTER
- parse:
attr: href
# NORMALIZE URL
- normalize:
routine: url
# LOAD PAGE LOCATED AT THAT URL
- walk:
to: value
do:
..
..
</code></pre>
</div>
<div id="if_3" class="col s12">
<pre class="language-yaml">
<code class="language-yaml"># FIND ALL `li`
- find:
path: li
do:
- parse
# CHECK IF THERE IS WORD `text` IN THE REGISTER
- if:
match: text
do:
# IF TRUE, SET OBJECT FIELD WITH THE VALUE OF THE REGISTER
- object_field_set:
object: someobj
field: somefield
# IF NOT FOUND, FIND `a`
else:
- find:
path: a
do:
# PARSE ATTRIBUTE `href` TO THE REGISTER
- parse:
attr: href
# NORMALIZE URL
- normalize:
routine: url
# LOAD PAGE LOCATED AT THAT URL
- walk:
to: value
do:
..
..
</code></pre>
</div>
</div>
<p class="flow-text">
Examples of <span class="hlt">gt</span>, <span class="hlt">lt</span>,
<span class="hlt">nlt</span>, <span class="hlt">eq</span> modes usage:
</p>
<div class="row">
<div class="col s12">
<ul class="tabs excdark">
<li class="tab col s3"><a class="active" href="#if_gt">gt</a></li>
<li class="tab col s3"><a href="#if_lt">lt</a></li>
<li class="tab col s3"><a href="#if_nlt">nlt</a></li>
<li class="tab col s3"><a href="#if_eq">eq</a></li>
</ul>
</div>
<div id="if_gt" class="col s12">
<pre class="language-yaml">
<code class="language-yaml"># FIND ALL `li`
- find:
path: li
do:
# PARSE ATTRIBUTE `id` VALUE AND EXTRACT ONLY DIGITS
- parse:
attr: id
filter:
- (\d+)
# CHECK IF VALUE OF THE REGISTER IS GREATER THAN `2`
- if:
gt: 2
# SPECIFY TYPE `integer`
type: int
do:
# IF ITS TRUE SET FIELD OF THE OBJECT TO THE REGISTER VALUE
- object_field_set:
object: someobj
field: somefield
</code></pre>
</div>
<div id="if_lt" class="col s12">
<pre class="language-yaml">
<code class="language-yaml"># FIND ALL `li`
- find:
path: li
do:
# PARSE ATTRIBUTE `id` VALUE AND EXTRACT ONLY DIGITS
- parse:
attr: id
filter:
- (\d+)
# CHECK IF VALUE OF THE REGISTER IS LESS THAN `2`
- if:
lt: 2
# SPECIFY TYPE `integer`
type: int
do:
# IF ITS TRUE SET FIELD OF THE OBJECT TO THE REGISTER VALUE
- object_field_set:
object: someobj
field: somefield
</code></pre>
</div>
<div id="if_nlt" class="col s12">
<pre class="language-yaml">
<code class="language-yaml"># НАЙДЕМ ВСЕ `li`
- find:
path: li
do:
# PARSE ATTRIBUTE `id` VALUE AND EXTRACT ONLY DIGITS
- parse:
attr: id
filter:
- (\d+)
# CHECK IF VALUE OF THE REGISTER IS NOT LESS (GREATER OR EQUAL) THAN `2`
- if:
nlt: 2
# SPECIFY TYPE `integer`
type: int
do:
# IF ITS TRUE SET FIELD OF THE OBJECT TO THE REGISTER VALUE
- object_field_set:
object: someobj
field: somefield
</code></pre>
</div>
<div id="if_eq" class="col s12">
<pre class="language-yaml">
<code class="language-yaml"># НАЙДЕМ ВСЕ `li`
- find:
path: li
do:
# PARSE ATTRIBUTE `id` VALUE AND EXTRACT ONLY DIGITS
- parse:
attr: id
filter:
- (\d+)
# CHECK IF VALUE OF THE REGISTER IS EQUAL `2`
- if:
eq: 1
# SPECIFY TYPE `integer`
type: int
else:
# IF ITS FALSE SET FIELD OF THE OBJECT TO THE REGISTER VALUE
- object_field_set:
object: someobj
field: somefield
</code></pre>
</div>
</div>
<p class="flow-text">
In the next chapter, you will learn how to use optical text recognition (OCR) and text extraction from images.
</p>
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