Dynamic evalution of python code by using string or code object

eval(object, global,local ) evalute valid python code

object: input object of string or code object
global: (optional ) global dictionary object
local: (optional ) local dictionary object

Using string object

my_str="x='plus2net'\nprint(x)"
eval(my_str)

Output

plus2net

Using code object

We create a code object by using compile()

cb=compile('print("Hello")', '', 'single')
eval(cb)

Output

Hello

Using restrictions

We can allow some functions in global scope only to evalute by using global option. Let us import our math module and find the sum of a iterable_object This will generate error as we have used one empty dictionary ( not allowing any method ) .

import math
str="print(math.fsum([1,2,3,4,5]))"
eval(str,{})

This will work as we have allowed math.fsum to execute. Output is 15.0

import math
str="print(fs([1,2,3,4,5]))"
eval(str,{'fs':math.fsum}) 3 15.0

builtin functions

eval() has full access to all builtin functions of Python. This code will not generate any error though we have supplied an empty dictionary ({}) to globals.

str="print(sum([1,2,3,4,5]))"
eval(str,{})  # 15

Note that sum() is a builtin function but fsum() is included in math module.

Take precaution by not allowing un-cleaned code to get executed through exec(). There is a potential danger in allowing codes to get executed without proper check.

All Built in Functions in Python dir() compile() exec() repr()

Math Functions math.fabs() Python- Tutorials

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