{"id":4437,"date":"2021-06-23T12:51:44","date_gmt":"2021-06-23T07:21:44","guid":{"rendered":"https:\/\/blog.guvi.in\/?p=4437"},"modified":"2025-10-28T14:40:45","modified_gmt":"2025-10-28T09:10:45","slug":"why-is-using-eval-a-bad-practice","status":"publish","type":"post","link":"https:\/\/www.guvi.in\/blog\/why-is-using-eval-a-bad-practice\/","title":{"rendered":"Why is using ‘eval’ a Bad Practice?"},"content":{"rendered":"\n

Are you using the eval<\/em><\/strong> function to evaluate the mathematical expression in Python? Yes, many of you might be. But do you even know that using eval can be a bad practice? <\/em> Now, if you are wondering why? Then probably you should stick around and understand this, with a couple of good examples, and get a solution for it.<\/p>\n\n\n\n\n\n

Why is using ‘eval’ a bad practice? <\/strong><\/em><\/h2>\n\n\n\n

It has been seen that the eval function starts deleting the system files and corrupts the system’s environment<\/strong>. Therefore, whenever you use the eval() function for executing the user input code, be careful.<\/p>\n\n\n\n

Moreover, make sure that you must check the user-entered data first, and when it looks fine only then go for it.<\/p>\n\n\n\n

Well, this blog will help you to find out the other reasons why eval can be a bad practice. Moreover, we have tried to detail the alternative functions that you can use at the place of eval.<\/p>\n\n\n\n

Do not worry. We have mentioned relevant examples with the details so that it will be more easy for you to understand the eval() function.<\/p>\n\n\n\n

Additionally, if you want to explore Python through a self-paced course, try HCL GUVI\u2019s Python self-paced course<\/strong><\/a>.<\/p>\n\n\n\n

Now that we understand why is using eval <\/em>a bad practice, let’s find out the essential details about the eval function.<\/p>\n\n\n\n

First, let’s take an overview of <\/strong>the eval <\/em><\/strong>function in Python!<\/strong><\/p>\n\n\n\n

What is an eval function in Python?<\/em><\/strong><\/h2>\n\n\n\n

eval <\/em><\/strong>is one of the built-in functions in Python. It parses the given argument and evaluates the expressions. <\/p>\n\n\n\n

Or simply, I can say that the eval <\/em>function in Python evaluates the “string<\/em>” <\/strong>as the expression and returns the output result as the “integer<\/em>“.<\/p>\n\n\n\n

Key point:<\/strong>
The eval <\/em>function of Python takes the string as “argument,” and evaluates it as the Python “expression.” The result of the Python expression is an “object.”<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The basic syntax of the eval <\/em>function is:<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n
expression:<\/em><\/strong> The string that is evaluated as the Python expression.globals (optional):<\/em><\/strong> The dictionary that specifies the global variables and methods.locals (optional):<\/em><\/strong> The dictionary that specifies the local variables and methods.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

What is the basic use of the eval function?<\/em><\/strong><\/h2>\n\n\n\n

This function uses when there is a requirement to evaluate mathematical expressions. Moreover, Python users use it to evaluate the string into codes.<\/p>\n\n\n\n

It is possible just because the eval <\/em><\/strong>function is evaluating the string expressions<\/em><\/strong> <\/strong>and returning the result in the form of an integer<\/em><\/strong>.<\/p>\n\n\n\n

Now, let’s take an example of how to use the eval<\/em> function in Python!<\/strong><\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

<\/p>\n\n\n\n

Input<\/strong><\/h3>\n\n\n\n

\u2018x**2\u2019<\/p>\n\n\n\n

\u20183\u2019<\/p>\n\n\n\n

Output:<\/strong><\/h3>\n\n\n\n

Enter the equation(in terms of x):x**2<\/p>\n\n\n\n

<type ‘str’><\/p>\n\n\n\n

Enter the value of x:3<\/p>\n\n\n\n

y = 9<\/p>\n\n\n\n

<type ‘int’><\/p>\n\n\n\n

NOTE: function_creator <\/strong>is one of those functions that evaluate the user-created mathematical functions.<\/p>\n\n\n\n

Moreover, you can see that the input is given as the string, and the output of the eval <\/em>function is in integer form.<\/p>\n\n\n\n

Now, let’s find out the reason why and how <\/strong>‘eval” <\/em><\/strong>can be a bad practice!!<\/strong><\/p>\n\n\n\n

In the above code, you can see that there is a function_creator <\/strong>that has few limitations. Like the user can call the function to get the hidden value of the program. This will happen because the eval <\/em>just executes whatever is passing to it.<\/p>\n\n\n\n

It will look like this:<\/strong><\/p>\n\n\n\n

Input:<\/strong><\/h3>\n\n\n\n

‘secret_function()’<\/p>\n\n\n\n

‘0’<\/p>\n\n\n\n

Output:<\/strong><\/h3>\n\n\n\n

Enter the equation(in terms of x):secret_function()<\/p>\n\n\n\n

Enter the value of x:0<\/p>\n\n\n\n

y = Secret key is 159<\/p>\n\n\n\n

This issue can also occur if you import the OS module in any of the Python programs. The portable way of OS allows us to utilize OS functionalities, such as write or read a file. <\/p>\n\n\n\n

It is quite dangerous to use as its single command can delete almost all the system files!!<\/p>\n\n\n\n

Now, you might be thinking why do I use it then? <\/em>Well, while writing the Python script for some applications like kiosk computers, web apps, and more, you need to take a risk to use it.<\/p>\n\n\n\n

Sum up: <\/strong>eval <\/em>can also be a bad practice because of the following reasons:
It is insecure and very dangerous. It is quite slow. Makes the process of debugging quite difficult.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Then, why do Python users still use the eval function?<\/em><\/strong><\/h2>\n\n\n\n

Well, eval <\/em>is not much in use as you might be thinking just because of security reasons.<\/p>\n\n\n\n

But in some situation, you may need to use it, like:<\/p>\n\n\n\n