inspect — Inspect live objects

The inspect module provides several useful functions to help get information about live objects such as modules, classes, methods, functions, tracebacks, frame objects, and code objects. For example, it can help you examine the contents of a class, retrieve the source code of a method, extract and format the argument list for a function, or get all the information you need to display a detailed traceback.

import inspect

Types and Members

You can easily check what type an object is at runtime.

import inspect

def my_func():
    pass

class MyClass:
    pass

print(inspect.isfunction(my_func)) # True
print(inspect.isclass(MyClass))    # True
print(inspect.ismodule(inspect))   # True

Retrieving Source Code

One of the most powerful features of inspect is the ability to read the actual source code of a live function directly from the file!

import inspect

def secret_calculator(a, b):
    # This is a highly classified algorithm!
    return (a * b) + 42

# 1. Get the actual lines of code as a string
code = inspect.getsource(secret_calculator)
print(code)

# 2. Get the file it was defined in
print(inspect.getfile(secret_calculator))

Function Signatures

You can dynamically inspect what arguments a function expects. This is heavily used by dependency injection frameworks (like FastAPI).

import inspect

def greet(name: str, age: int = 18, *args, **kwargs):
    pass

sig = inspect.signature(greet)

for param_name, param in sig.parameters.items():
    print(f"Name: {param_name}, Type: {param.annotation}, Default: {param.default}")

# Output:
# Name: name, Type: <class 'str'>, Default: <class 'inspect._empty'>
# Name: age, Type: <class 'int'>, Default: 18
# Name: args, Type: <class 'inspect._empty'>, Default: <class 'inspect._empty'>
# Name: kwargs, Type: <class 'inspect._empty'>, Default: <class 'inspect._empty'>

API Reference

Checking Types

Retrieving Source

Inspecting Signatures