Python Inspect Module

In this tutorial, we will learn about the Python's inspect module and its functions. It module is used to examine the objects within our code. As we know, Python operates as an object-oriented language and our code revolves around these objects, the inspect module becomes valuable for identifying particular modules or objects. It proves particularly useful for examining specific function calls or tracebacks, which in turn facilitates smoother debugging processes.

The inspect module offers a range of methods that can be divided into two main categories: methods for confirming the type of token, and methods for fetching the source of the token.

Methods to verify the type of Token

Below are the methods to verify the type of the token -

isclass(): This method returns a True value if the object is a class; otherwise, it returns False. When used in combination with the getmembers() function, it displays both the class and its type. This method is used to examine active classes.

Let's understand the following example -

Example -

import inspect

class MyClass:
    pass
def my_function():
    pass

result_class = inspect.isclass(MyClass)
result_function = inspect.isclass(my_function)

print("Is MyClass a class - ", result_class)
print("Is my_function a class - ", result_function)

Output:

Is MyClass a class - True
Is my_function a class -  False

In this example, the isclass() method is used to check whether the MyClass and my_function objects are classes. The results will be True for MyClass (since it's a class) and False for my_function (since it's not a class).

ismodule(): If the provided argument is a module that has been imported, this function gives a True response.

Example -

import inspect
import math
result_math = inspect.ismodule(math)
result_str = inspect.ismodule("hello")

print("Is math a module - ", result_math)
print("Is 'hello' a module - ", result_str)

Output:

Is math a module - True
Is 'hello' a module - False

isfunction() - If the provided argument is a built-in function name, this method returns a True result.

Example -

import inspect

def my_function():
    pass

result_my_function = inspect.isfunction(my_function)
result_print = inspect.isfunction(print)

print("Is my_function a function - ", result_my_function)
print("Is print a function - ", result_print)

Output:

Is my_function a function - True
Is print a function - True

ismethod() - This function is employed to determine if the provided argument corresponds to the name of a method or not.

Example -

import inspect
class MyClass:
    def my_method(self):
        pass

obj = MyClass()
result_method = inspect.ismethod(obj.my_method)
result_function = inspect.ismethod(my_function)

print("Is my_method a method -", result_method)
print("Is my_function a method - ", result_function)

Output:

Is my_method a method -  True
Is my_function a method -  False

Method to Retrieves the Source of Token

getclasstree(): The getclasstree()` function is useful for obtaining and examining the hierarchy of classes. It provides a tuple that includes the class itself and its parent classes. When paired with the getmro() function, which returns the parent classes, it aids in comprehending the class hierarchy.

Example -

import inspect

class A:
    pass

class B(A):
    pass

class C(B):
    pass

class D(C):
    pass

tree = inspect.getclasstree([D, B], unique=True)
print(tree)

Output:

[(<class '__main__.D'>, (<class '__main__.C'>,)), (<class '__main__.B'>, (<class '__main__.A'>,))]

Explanation -

In the above code -

We define four classes: A, B, C, and D. Each class is a child of its preceding class, following the inheritance hierarchy.
The `inspect.getclasstree()` function is used to retrieve the class hierarchy of two specified classes: D and B. The parameter `unique=True` ensures that duplicate classes are not repeated in the hierarchy.
The output of the `inspect.getclasstree()` function call is presented as a list of tuples, where each tuple contains a class and its parent classes. The tuples are structured to represent the inheritance chain. In the output, it's evident that class D is derived from class C, which in turn is derived from class B, and class B is derived from class A.

getmembers(): This function provides a list of member functions found in the module given as an argument to this function.

Example:

import inspect

def my_function():
    pass

class MyClass:
    def my_method(self):
        pass

members_function = inspect.getmembers(my_function)
members_class = inspect.getmembers(MyClass)

print("Members of my_function:", members_function)
print("Members of MyClass:", members_class)

Output:

Members of my_function: [('__annotations__', {}), ('__call__', <method-wrapper '__call__' of function object at 0x7f3d91d76ca0>), ('__class__', <class 'function'>), ... ]
Members of MyClass: [('__class__', <class 'type'>), ('__delattr__', <slot wrapper '__delattr__' of 'object' objects>), ('__dict__', <attribute '__dict__' of 'MyClass' objects>), ... ]

In this code, the `getmembers()` function is used to retrieve the members of both the `my_function` function and the `MyClass` class. The output displays the list of members for each of these entities.

We can also get the members of a module.

Example - 2:

import inspect
import time
# shows the member functions
# of any module or object
print(inspect.getmembers(time))

Output:

[('CLOCK_BOOTTIME', 7), ('CLOCK_MONOTONIC', 1), ('CLOCK_MONOTONIC_RAW', 4), ('CLOCK_PROCESS_CPUTIME_ID', 2), ('CLOCK_REALTIME', 0), ('CLOCK_TAI', 11), ('CLOCK_THREAD_CPUTIME_ID', 3), ('_STRUCT_TM_ITEMS', 11), ('__doc__', 'This module provides various functions to manipulate time values.\n\nThere are two standard representations of time.  One is the number\nof seconds since the Epoch, in UTC (a.k.a. GMT).  It may be an integer\nor a floating point number (to represent fractions of seconds).\nThe Epoch is system-defined; on Unix, it is generally January 1st, 1970.\nThe actual value can be retrieved by calling gmtime(0).\n\nThe other representation is a tuple of 9 integers giving local time.\nThe tuple items are:\n  year (including century, e.g. 1998)\n  month (1-12)\n  day (1-31)\n  hours (0-23)\n  minutes (0-59)\n  seconds (0-59)\n  weekday (0-6, Monday is 0)\n  Julian day (day in the year, 1-366)\n  DST (Daylight Savings Time) flag (-1, 0 or 1)\nIf the DST flag is 0, the time is given in the regular time zone;\nif it is 1, the time is given in the DST time zone;\nif it is -1, mktime() should guess based on the date and time.\n'), ('__loader__', <class '_frozen_importlib.BuiltinImporter'>), ('__name__', 'time'), ('__package__', ''), ('__spec__', ModuleSpec(name='time', loader=<class '_frozen_importlib.BuiltinImporter'>, origin='built-in')), ('altzone', 0), ('asctime', <built-in function asctime>), ('clock_getres', <built-in function clock_getres>), ('clock_gettime', <built-in function clock_gettime>), ('clock_gettime_ns', <built-in function clock_gettime_ns>), ('clock_settime', <built-in function clock_settime>), ('clock_settime_ns', <built-in function clock_settime_ns>), ('ctime', <built-in function ctime>), ('daylight', 0), ('get_clock_info', <built-in function get_clock_info>), ('gmtime', <built-in function gmtime>), ('localtime', <built-in function localtime>), ('mktime', <built-in function mktime>), ('monotonic', <built-in function monotonic>), ('monotonic_ns', <built-in function monotonic_ns>), ('perf_counter', <built-in function perf_counter>), ('perf_counter_ns', <built-in function perf_counter_ns>), ('process_time', <built-in function process_time>), ('process_time_ns', <built-in function process_time_ns>), ('pthread_getcpuclockid', <built-in function pthread_getcpuclockid>), ('sleep', <built-in function sleep>), ('strftime', <built-in function strftime>), ('strptime', <built-in function strptime>), ('struct_time', <class 'time.struct_time'>), ('thread_time', <built-in function thread_time>), ('thread_time_ns', <built-in function thread_time_ns>), ('time', <built-in function time>), ('time_ns', <built-in function time_ns>), ('timezone', 0), ('tzname', ('UTC', 'UTC')), ('tzset', <built-in function tzset>)]

signature(): The `signature()` function aids users in comprehending the attributes that need to be provided to a function.

Example:

import inspect
def my_function(x, y=0, *args, **kwargs):
    pass
signature_result = inspect.signature(my_function)
print("Function signature:", signature_result)

Output:

Function signature: (x, y=0, *args, **kwargs)

In this example, the `signature()` function is utilized to determine the signature of the my_function() function. The output displays the signature of the function, including its parameters and special argument types.

stack(): The `stack()` function assists in inspecting the interpreter stack, revealing the sequence in which functions were invoked.

Example -

import inspect

def function_one():
    function_two()

def function_two():
    stack_result = inspect.stack()
    print("Function call stack:", stack_result)

function_one()

Output:

Function call stack: [FrameInfo(frame=<frame at 0x7f785c0ad8e0, file 'example.py', line 6, code function function_two>, filename='example.py', lineno=6, function='function_two', code_context=['    function_two()\n'], index=0), ...]

In this example, the `stack()` function is used to retrieve and display information about the call stack. The output provides details about the frames in the stack, including file locations, line numbers, and function names.

Example - 2:

import inspect

def fibonacci(n):
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fibonacci(n - 1) + fibonacci(n - 2)

def main():
    stack_result = inspect.stack()
    print("Function call stack:", stack_result)
    
    result = fibonacci(5)
    print("Fibonacci result:", result)

main()

Output:

Function call stack: [FrameInfo(frame=<frame at 0x7f6d59cc0b80, file '<string>', line 13, code main>, filename='<string>', lineno=12, function='main', code_context=None, index=None, positions=Positions(lineno=12, end_lineno=12, col_offset=19, end_col_offset=34)), FrameInfo(frame=<frame at 0x7f6d59a22ca0, file '<string>', line 18, code <module>>, filename='<string>', lineno=18, function='<module>', code_context=None, index=None, positions=Positions(lineno=18, end_lineno=18, col_offset=0, end_col_offset=6))]
Fibonacci result: 5

getsource() - The getsource() function retrieves the source code of a specified module, class, method, or function.

Example -

import inspec
class MyClass:
    def __init__(self, value):
        self.value = value

    def get_value(self):
        return self.value

source_code = inspect.getsource(MyClass)

print("Source code of MyClass:")
print(source_code)

Output:

Source code of MyClass:
class MyClass:
    def __init__(self, value):
        self.value = value

    def get_value(self):
        return self.value

In this example, the `getsource()` function is utilized to retrieve and display the source code of the `MyClass` class. The output presents the source code of the class, including its methods and attributes.

getmodule() - The `getmodule()` function provides the module name associated with a specific object passed as an argument.

Example -

import inspect

def my_function():
    pass

module_name = inspect.getmodule(my_function).__name__
print("Module name of my_function:", module_name)

Output:

Module name of my_function: __main__

In this example, the `getmodule()` function is used to retrieve the module name of the `my_function` function. The output displays the name of the module in which the function is defined.

getdoc(): The `getdoc()` function provides the documentation of the specified object passed as an argument, presented as a string.

Example:

import inspect
def my_function():
    """This is a sample function."""
    pass

documentation = inspect.getdoc(my_function)

print("Documentation of my_function:")
print(documentation)

Output:

Documentation of my_function:
This is a sample function.

Conclusion

In conclusion, the `inspect` module is a very useful library for Python programmers. It helps them look closely at different parts of their code, like classes, functions, and more. This allows the developer to understand what's happening inside and fix any problems. Whether they want to check out how things are connected, see the actual code, or understand how functions work, the `inspect` module has got them covered.

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