# Flask – Variable Rules

It is possible to build a URL dynamically, by adding variable parts to the rule parameter. This variable part is marked as **<variable-name>**. It is passed as a keyword argument to the function with which the rule is associated.

In the following example, the rule parameter of **route()** decorator contains **<name>** variable part attached to URL **‘/hello’**. Hence, if the **http://localhost:5000/hello/TutorialsPoint** is entered as a **URL** in the browser, **‘TutorialPoint’** will be supplied to **hello()** function as argument.

```
from flask import Flask
app = Flask(__name__)

@app.route('/hello/<name>')
def hello_name(name):
   return 'Hello %s!' % name

if __name__ == '__main__':
   app.run(debug = True)
```

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</div>Save the above script as **hello.py** and run it from Python shell. Next, open the browser and enter URL **http://localhost:5000/hello/TutorialsPoint.**

The following output will be displayed in the browser.

```
Hello TutorialsPoint!
```

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</div>In addition to the default string variable part, rules can be constructed using the following converters −

<table class="table table-bordered" id="bkmrk-sr.no.-converters-%26-"><tbody><tr><th width="10%">Sr.No.</th><th class="ts">Converters &amp; Description</th></tr><tr><td class="ts">1</td><td>**int**

accepts integer

</td></tr><tr><td class="ts">2</td><td>**float**

For floating point value

</td></tr><tr><td class="ts">3</td><td>**path**

accepts slashes used as directory separator character

</td></tr></tbody></table>

In the following code, all these constructors are used.

```
from flask import Flask
app = Flask(__name__)

@app.route('/blog/<int:postID>')
def show_blog(postID):
   return 'Blog Number %d' % postID

@app.route('/rev/<float:revNo>')
def revision(revNo):
   return 'Revision Number %f' % revNo

if __name__ == '__main__':
   app.run()
```

<div class="open_grepper_editor" id="bkmrk--1" title="Edit & Save To Grepper">  
</div>Run the above code from Python Shell. Visit the URL **http://localhost:5000/blog/11** in the browser.

The given number is used as argument to the **show\_blog()** function. The browser displays the following output −

```
Blog Number 11
```

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</div>Enter this URL in the browser − **http://localhost:5000/rev/1.1**

The **revision()** function takes up the floating point number as argument. The following result appears in the browser window −

```
Revision Number 1.100000
```

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</div>The URL rules of Flask are based on **Werkzeug’s** routing module. This ensures that the URLs formed are unique and based on precedents laid down by Apache.

Consider the rules defined in the following script −

```
from flask import Flask
app = Flask(__name__)

@app.route('/flask')
def hello_flask():
   return 'Hello Flask'

@app.route('/python/')
def hello_python():
   return 'Hello Python'

if __name__ == '__main__':
   app.run()
```

<div class="open_grepper_editor" id="bkmrk--4" title="Edit & Save To Grepper">  
</div>Both the rules appear similar but in the second rule, trailing slash **(/)** is used. As a result, it becomes a canonical URL. Hence, using <u>**/python**</u> or <u>**/python/**</u> returns the same output. However, in case of the first rule, <u>**/flask/**</u> URL results in <u>**404 Not Found**</u> page.