What is the difference between "exec" and "eval" in Python?

In Python, both exec() and eval() functions are used for executing dynamically generated Python code or expressions, but they have some key differences:


  • exec(): It is used for executing statements or blocks of code, which may include multiple lines and have side effects (e.g., variable assignments, function definitions, etc.). exec() does not return a value.
  • eval(): It is used for evaluating a single expression and returning its result. It is mainly used for mathematical or logical computations and returns the computed value.

Input Format:

  • exec(): It takes a string or a code object as input and executes it as Python code.
  • eval(): It takes a string or an expression as input and evaluates it as a Python expression, returning the computed result.


  • exec(): It does not return any value explicitly. However, it can modify the global and local namespaces, produce side effects, or perform operations based on the executed code.
  • eval(): It returns the computed value of the evaluated expression.


  • exec(): It is suitable for executing code blocks, running scripts, or performing dynamic code generation.
  • eval(): It is useful when you want to evaluate mathematical or logical expressions provided as strings or when you need to dynamically compute values based on expressions.

Here's an example to illustrate the difference between exec() and eval():

code = '''
x = 10
y = 20
result = x + y

exec(code)  # Executes the code block defined in 'code' string

expr = 'x * y + 5'
computed_value = eval(expr)  # Evaluates the expression and returns the computed value

print(result)  # Output: 30
print(computed_value)  # Output: 205

In this example, the exec() function executes the code block defined in the code string, modifying the global and local namespaces. The eval() function evaluates the expression in the expr string and returns the computed value.

It's worth noting that both exec() and eval() should be used with caution, especially when executing code from untrusted or unsanitized sources. Executing arbitrary code can pose security risks and lead to unintended consequences. Therefore, it's important to ensure that you only execute trusted code or perform appropriate security checks.

Overall, exec() and eval() provide different functionalities and are used in different scenarios based on the desired outcome, whether it's executing code blocks or evaluating expressions, respectively.

Related Questions You Might Be Interested