How to call a function of a module by using its name (a string) in Python?

To call a function from a module using its name as a string in Python, you can use a combination of getattr() (to dynamically fetch the function) and importlib (to import the module by name if needed). Here’s how to do it:

1. If the Module is Already Imported

Use getattr() on the imported module object:

import math  # Example module

function_name = "sqrt"  # Name of the function as a string
func = getattr(math, function_name)  # Get the function reference

result = func(25)  # Call the function
print(result)  # Output: 5.0

2. If the Module Name is Also a String

Use importlib.import_module() to dynamically import the module:

import importlib

module_name = "math"  # Name of the module as a string
function_name = "sqrt"

# Import the module dynamically
module = importlib.import_module(module_name)

# Get the function and call it
func = getattr(module, function_name)
result = func(25)
print(result)  # Output: 5.0

3. For Functions in the Current Module

Use globals() to access the current module’s functions:

def greet():
    return "Hello, World!"

function_name = "greet"
func = globals()[function_name]  # Get the function from the global scope

print(func())  # Output: Hello, World!

4. Handling Optional Parameters and Arguments

Pass arguments dynamically using *args and **kwargs:

import math

function_name = "pow"
func = getattr(math, function_name)

# Call pow(2, 3) = 8
result = func(2, 3)
print(result)  # Output: 8.0

5. Error Handling

Check if the function exists before calling it:

module = importlib.import_module("math")
function_name = "invalid_function"

if hasattr(module, function_name):
    func = getattr(module, function_name)
    func()
else:
    print(f"Function '{function_name}' not found in module.")

6. Security Considerations

Avoid using this approach with untrusted input (e.g., user-provided strings), as it can lead to code execution vulnerabilities. If security is a concern, use a predefined allowlist of allowed functions:

# Safe allowlist approach
ALLOWED_FUNCTIONS = {"sqrt", "log", "sin"}

function_name = "sqrt"  # User-provided input
if function_name in ALLOWED_FUNCTIONS:
    func = getattr(math, function_name)
    result = func(25)
else:
    print("Function not allowed.")

Full Example

import importlib

def call_function(module_name, function_name, *args, **kwargs):
    try:
        module = importlib.import_module(module_name)
        func = getattr(module, function_name)
        return func(*args, **kwargs)
    except ImportError:
        print(f"Module '{module_name}' not found.")
    except AttributeError:
        print(f"Function '{function_name}' not found in module '{module_name}'.")

# Example usage
result = call_function("math", "sqrt", 25)
print(result)  # Output: 5.0

Key Notes

• getattr(): Fetches attributes (like functions) from objects (modules, classes, etc.).
• importlib.import_module(): Safely imports modules by name (as a string).
• Security: Never use this with untrusted input unless properly validated.
• Error Handling: Always handle ImportError (invalid module) and AttributeError (invalid function).