Inspect live objects in Python

The inspect module in Python provides powerful functions to examine live objects such as modules, classes, methods, functions, and code objects. These functions perform type checking, retrieve source code, inspect classes and functions, and examine the interpreter stack.

Key Functions

getmembers() − Returns all members of an object in a list of name-value pairs sorted by name. Optional predicate parameter filters results.

getmodulename() − Returns the module name from a file path, excluding enclosing package names.

Example Module

Let's create a sample module to demonstrate inspect functionality ?

# inspect_example.py
'''This is module docstring'''

def hello():
    '''hello docstring'''
    print('Hello world')
    return

# Class definitions
class parent:
    '''parent docstring'''
    def __init__(self):
        self.var = 'hello'
    
    def hello(self):
        print(self.var)

class child(parent):
    def hello(self):
        '''hello function overridden'''
        super().hello()
        print("How are you?")

Using getmembers()

Get all non-private members of the module ?

import inspect
import inspect_example

for name, obj in inspect.getmembers(inspect_example):
    if not name.startswith('__'):
        print(name, obj)

child <class 'inspect_example.child'>
hello <function hello at 0x...>
parent <class 'inspect_example.parent'>

Predicates

Predicates are logical conditions that filter objects based on their type. The inspect module provides several built-in predicates ?

Example: Getting Only Classes

import inspect
import inspect_example

for name, obj in inspect.getmembers(inspect_example, inspect.isclass):
    print(name, obj)

child <class 'inspect_example.child'>
parent <class 'inspect_example.parent'>

Retrieving Documentation

Use getdoc() to retrieve docstrings from modules, classes, or functions ?

import inspect
import inspect_example

print("Module docstring:", inspect.getdoc(inspect_example))
print("Class docstring:", inspect.getdoc(inspect_example.parent))
print("Function docstring:", inspect.getdoc(inspect_example.hello))

Module docstring: This is module docstring
Class docstring: parent docstring
Function docstring: hello docstring

Getting Source Code

Use getsource() to retrieve the source code of functions and classes ?

import inspect
import inspect_example

print(inspect.getsource(inspect_example.hello))

def hello():
    '''hello docstring'''
    print('Hello world')
    return

Function Signatures

Examine function signatures using signature() ?

import inspect
import inspect_example

sig = inspect.signature(inspect_example.parent.hello)
print("Signature:", sig)

Signature: (self)

Command Line Interface

The inspect module also provides command-line functionality to examine modules and functions directly from the terminal.

To inspect a module ?

python -m inspect -d inspect_example

To view source code of a specific function ?

python -m inspect inspect_example:hello

Conclusion

The inspect module is essential for debugging, documentation generation, and dynamic code analysis. Use getmembers() with predicates to filter objects, getdoc() for documentation, and getsource() for source code examination.