Related Articles
Implement IsNumber() function in Python
• Last Updated : 06 May, 2021

In this article we will see how to implement isNumber() method using Python. This method takes in a string as input and returns True or False according to whether the string is a number or not.
Examples:

```Input :  "12345"
Output :  True

Input : "-12345"
Output : True

Input : "abc"
Output : False```

Approach :
Here we will take advantage of the int() built-in function available in Python. Also with this approach we will see how Exception Handling comes to our aid. Using try-catch construct we try to convert the string to integer. In case the string cannot be converted the handler catches the exception that is thrown.
Below is the Implementation:

## Python3

 `# Implementation of isNumber() function``def` `isNumber(s):``    ` `    ``# handle for negative values``    ``negative ``=` `False``    ``if``(s[``0``] ``=``=``'-'``):``        ``negative ``=` `True``        ` `    ``if` `negative ``=``=` `True``:``        ``s ``=` `s[``1``:]``    ` `    ``# try to convert the string to int``    ``try``:``        ``n ``=` `int``(s)``        ``return` `True``    ``# catch exception if cannot be converted``    ``except` `ValueError:``        ``return` `False``        ` `    ` `s1 ``=` `"9748513"``s2 ``=` `"-9748513"``s3 ``=` `"GeeksforGeeks"` `print``(``"For input '{}' isNumber() returned : {}"``.``format``(s1, isNumber(s1)))``print``(``"For input '{}' isNumber() returned : {}"``.``format``(s2, isNumber(s2)))``print``(``"For input '{}' isNumber() returned : {}"``.``format``(s3, isNumber(s3)))`

Output :

```For input '9748513' isNumber() returned : True
For input '-9748513' isNumber() returned : True
For input 'GeeksforGeeks' isNumber() returned : False```

Note : This is not the only way to implement the isNumber() function but it is arguably the fastest way of doing so. Try/Catch doesn’t introduce much overhead because the most common exception is caught without an extensive search of stack frames.

Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course. And to begin with your Machine Learning Journey, join the Machine Learning – Basic Level Course

My Personal Notes arrow_drop_up