Python Eval function – Example and Uses

Do you ever dream of putting a queen robe in an old fairy basket and suddenly wishing it to become a trendy gold studded robe? This is, of course, a dream coming true, but what if I tell you this can actually happen.

Surprised? This fairy basket if replaced by our buddy python, then I’m not afraid to tell you all that it can actually do this. How? Here is an article where our buddy Python just suddenly turns out to be a fairy for it’s coder with a magic wand spelling out a magic rhyme. Let us learn about Python Eval Function.

Python Eval function

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Python Eval Function

Speak after me

‘ Dear coder, after this nobody will be your rival
Lemme tell you a secret of eval. ‘

As I had stated earlier, Python uses Eval as a magic spell, but for what? So technically ‘eval function parses the expression argument and evaluates it as a python expression’. But in a straight and simple language, it evaluates the simple old robe and generates a completely different yet required gold studded one. This simple robe is STRING and this new robe is INTEGER.

The syntax of the Eval function is:

  • eval(expression, [globals[, locals]])

For Example:

def drivingage(age):
    if age>18:
        print("yes")
    else:
        print("no")
age=int(input("age"))
drivingage(age)

Output

age 6
no

Argument  and Parameters of Eval Function in Python

The arguments or parameters of eval function are STRING (global and locals can be used as an argument inside eval function), but the globals must be represented as a dictionary and the locals as a mapped object. This is very same as the robe can be of silk or cotton but silk should be ____ while cotton should be ____

Return Value of Python Eval Function

The result/return value will mostly be integer. Its like “Use any (silk/cotton) you’ll get a gold studded robe only”.

Let’s have a look at the basic code :

Example of Python Eval Function

a=int(input(“enter a number of choice”))
if:
   a = 1
   print(eval('a + 1'))
Else:
   break()
print(“the program is executed”)

Output

2

Python Eval Example

a=eval(“2** 5”))
print(a)

Output

32

Python Eval() Example

a=eval("sum([9,7])")
print(a)

Output

16

Python making a cool robe has an easy code though 🙂

Where do we use EVAL()?

To answer this question, the basic answer is Python, but the technical answer is in that code of Python where the coder wants to evaluate mathematical expression or evaluation of string.

WHEN should a coder use Eval?

Not every spell is useful everywhere similarly, eval should be used in scripting in a Python program for real-time evaluation.

Python Eval() Parameters

The eval() function takes three parameters:

  • expression – string parsed and evaluated as a Python expression
  • globals (optional) – is a dictionary
  • locals (optional)- mapping object. Dictionary is the standard and is a commonly used mapping type in Python.

Exploiting Eval in Python

Having a function in your code that returns some kind of password or other confidential data can be serious. A user can make a call to this function through Python eval() and make their way to sensitive data. How would you like a user to be able to read and write your files, or worse, delete them or even redo them? This is possible using the command os.system(‘rm -rf *’). This poses higher risks when working with applications like web apps and kiosk computers.

Warnings while using eval() in Python

A situation where you are using a Unix system (macOS, Linux etc) and you have imported the os module. The os module provides a portable way to use operating system functionalities such as reading or writing to a file.

Summary

This fairy basket has so much more to offer, and Eval was just one magical spell. We’ll learn from others too. Having learned so much about Eval that the need to have a fairy wand is so much less now. Haha, so let’s end this topic with a concentrated read, practicing a code, learning while relaxing and enjoying coding. Hope this article proved to be beneficial for everyone searching for the usage of eval.

Thank you for a good read, keep coding, keep learning, and also keep understanding the fairy basket. Happy Pythoning 🙂

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