Python eval
Python eval() builtin function is used to evaluate an expression that is given as a string. eval() can also execute code objects created by compile() method.
In this tutorial, we will learn about the syntax of Python eval() function, and learn how to use this function with the help of examples.
Syntax
The syntax of eval() function is
eval(expression[, globals[, locals]])
where
| Parameter | Required/Optional | Description |
|---|---|---|
| expression | Required | A string. This expression is parsed and evaluated as a Python expression. |
| globals | Optional | A dictionary. This is used as global namespace. |
| locals | Optional | Any mapping object. This is used as local namespace. |
Returns
The function returns value of the given expression.
Examples
1 Evaluate an Expression
In this example, we take a Python expression in a string, and pass it to eval() function for evaluation.
Python Program
x = 10
expression = 'x + 5'
result = eval(expression)
print("Result :", result)
Output
Result : 15
2 Evaluate an Expression with Builtin Function
In this example, we take a Python expression in a string where the expression uses Python builtin function pow(), and pass it to eval() function for evaluation.
Python Program
x = 10
expression = 'pow(x, 3)'
result = eval(expression)
print("Result :", result)
Output
Result : 1000
3 Evaluate an Expression with Global Values
In this example, we provide globals parameter to eval() function. Values for the variables in this dictionary are used for expression evaluation.
Python Program
x = 10
expression = 'pow(x, 3)'
globals = {'x': 5}
result = eval(expression, globals)
print("Result :", result)
Output
Result : 125
4 Evaluate an Expression with Syntax Errors
If there are any syntax errors while parsing the expression, an exception is raised.
Python Program
x = 10
expression = 'x - a'
result = eval(expression)
print("Result :", result)
Output
NameError: name 'a' is not defined
Conclusion
In this Python Tutorial, we have learnt the syntax of Python eval() builtin function, and also learned how to use this function, with the help of Python example programs.