Python eval() and exec() functions

eval() and exec() are built-in Python functions that allow you to dynamically execute code. They can be helpful in some specific cases, but they also pose security risks if used improperly.

Here's a tutorial on eval() and exec() functions in Python:

eval()

eval() is a built-in Python function that takes a single argument, which is a string containing a Python expression. It evaluates the expression and returns the result:

expression = "2 + 3 * 5"
result = eval(expression)
print(result)  # Output: 17

Keep in mind that eval() should only be used with trusted input, as it can execute any arbitrary code, potentially leading to security vulnerabilities.

exec()

exec() is another built-in Python function that takes a single argument, which is a string containing one or more lines of Python code. It dynamically executes the code, but unlike eval(), it does not return any value. exec() is used for executing statements, rather than evaluating expressions:

code = """
x = 5
y = 3
result = x * y
"""

exec(code)
print(result)  # Output: 15

As with eval(), you should only use exec() with trusted input, as it can execute any arbitrary code and potentially lead to security vulnerabilities.

Differences between eval() and exec()

eval() evaluates a single expression and returns its value, while exec() executes one or more lines of code and does not return a value.
eval() is meant for evaluating expressions, whereas exec() is meant for executing statements.

Scope and exec()

By default, exec() executes code in the current scope. However, you can provide an optional dictionary for global and/or local namespaces:

globals_dict = {"x": 2, "y": 3}
locals_dict = {}

code = "result = x * y"
exec(code, globals_dict, locals_dict)

print(locals_dict["result"])  # Output: 6

In this example, exec() is provided with globals_dict and locals_dict dictionaries for global and local namespaces, respectively. The code is executed in the context of these dictionaries, and the result variable is stored in locals_dict.

Security considerations

Both eval() and exec() can execute arbitrary Python code, which can lead to security vulnerabilities if used with untrusted input. You should only use these functions with trusted input, or consider alternatives like ast.literal_eval() for safely parsing and evaluating simple expressions.

In summary, eval() and exec() are built-in Python functions that allow you to dynamically evaluate expressions and execute code, respectively. While they can be useful in some specific cases, they pose security risks if used improperly. Always use these functions with caution and only with trusted input.

How to use eval() for expression evaluation in Python:
- Description: Utilize eval() to evaluate expressions provided as strings.
- Code:
```
result = eval("2 + 3")
```
Dynamic code execution with eval() in Python:
- Description: Dynamically execute Python code by evaluating strings containing valid Python expressions.
- Code:
```
code = "print('Hello, World!')"
eval(code)
```
String to code conversion with eval() in Python:
- Description: Convert strings containing Python expressions into executable code.
- Code:
```
expression = "2 * 5"
result = eval(expression)
```
Executing dynamic code blocks with exec() in Python:
- Description: Use exec() for executing dynamic code blocks or entire Python scripts.
- Code:
```
code_block = """
for i in range(5):
    print(i)
"""
exec(code_block)
```
String to code conversion with exec() in Python:
- Description: Convert strings containing Python code into executable code using exec().
- Code:
```
code_string = """
def greet(name):
    print(f"Hello, {name}!")
"""
exec(code_string)
```