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Python: eval() function

eval() function

The eval() function is used to evaluate the specified expression. If the expression is a correct Python statement, it will be executed.

Version:

(Python 3)

Syntax:

eval(expression, globals=None, locals=None)

Parameter:

Name Description Required /
Optional
expression A string as parsed that will evaluated as a Python expression. Required
globals A dictionary Optional
locals A mapping object. Optional

Example: Python eval() function 

x = 5
print(eval('x+1'))
print(eval('x'))

Output:

6
5

Example: Passing empty dictionary as globals parameter

from math import *
print(eval('dir()', {}))

#Following code will raise an exception
print(eval('sqrt(36)', {}))

Output:

['__builtins__']
Traceback (most recent call last):
  File "/tmp/sessions/5cb89b87138fc37f/main.py", line 5, in 
    print(eval('sqrt(36)', {}))
  File "", line 1, in 
NameError: name 'sqrt' is not defined

Python Code Editor:

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os 
dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os
cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

  • The os and os.path modules.
  • The __file__ constant
  • os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
  • os.path.dirname(path) (returns "the directory name of pathname path")
  • os.getcwd() (returns "a string representing the current working directory")
  • os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m