dir() function in Python

dir() is a powerful inbuilt function in Python3, which returns list of the attributes and methods of any object (say functions , modules, strings, lists, dictionaries etc.)
Syntax :

dir({object})

Parameters :

object [optional] : Takes object name

Returns :
dir() tries to return a valid list of attributes of the object it is called upon. Also, dir() function behaves rather differently with different type of objects, as it aims to produce the most relevant one, rather than the complete information. 

• For Class Objects, it returns a list of names of all the valid attributes and base attributes as well. 
  
• For Modules/Library objects, it tries to return a list of names of all the attributes, contained in that module. 
  
• If no parameters are passed it returns a list of names in the current local scope.

Code #1 : With and Without importing external libraries.

Python3

# Python3 code to demonstrate dir()
# when no parameters are passed

# Note that we have not imported any modules
print(dir())


# Now let's import two modules
import random
import math

# return the module names added to
# the local namespace including all
# the existing ones as before
print(dir())

Output :

['__builtins__', '__cached__', '__doc__', '__file__', '__loader__',
                                          '__name__', '__package__', '__spec__']



['__builtins__', '__cached__', '__doc__', '__file__', '__loader__',
                         '__name__', '__package__', '__spec__', 'math', 'random']

Code #2 :

Python3

# Python3 code to demonstrate dir() function
# when a module Object is passed as parameter.

# import the random module
import random


# Prints list which contains names of
# attributes in random function
print("The contents of the random library are::")

# module Object is passed as parameter
print(dir(random))

Output :

The contents of the random library are ::

['BPF', 'LOG4', 'NV_MAGICCONST', 'RECIP_BPF', 'Random', 'SG_MAGICCONST',
'SystemRandom', 'TWOPI', '_BuiltinMethodType', '_MethodType', '_Sequence',
'_Set', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__',
'__name__', '__package__', '__spec__', '_acos', '_ceil', '_cos', '_e', '_exp',
'_inst', '_log', '_pi', '_random', '_sha512', '_sin', '_sqrt', '_test', '_test_generator',
'_urandom', '_warn', 'betavariate', 'choice', 'expovariate', 'gammavariate', 'gauss',
'getrandbits', 'getstate', 'lognormvariate', 'normalvariate', 'paretovariate', 'randint',
'random', 'randrange', 'sample', 'seed', 'setstate', 'shuffle', 'triangular', 'uniform',
'vonmisesvariate', 'weibullvariate']

Code #3 : Object is passed as parameters.

Python3

# When a list object is passed as
# parameters for the dir() function

# A list, which contains
# a few random values
geeks = ["geeksforgeeks", "gfg", "Computer Science",
                    "Data Structures", "Algorithms" ]


# dir() will also list out common
# attributes of the dictionary
d = {}   # empty dictionary

# dir() will return all the available
# list methods in current local scope
print(dir(geeks))


# Call dir() with the dictionary
# name "d" as parameter. Return all
# the available dict methods in the
# current local scope
print(dir(d))

Output :

['__add__', '__class__', '__contains__', '__delattr__', '__delitem__',
'__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', 
'__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', 
'__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', 
'__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', 
'__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 
'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']


['__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', 
'__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', 
'__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', 
'__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setitem__', 
'__sizeof__', '__str__', '__subclasshook__', 'clear', 'copy', 'fromkeys', 'get', 'items', 
'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']

Code #4 : User Defined – Class Object with an available __dir()__ method is passed as parameter. 

Python3

# Python3 program to demonstrate working
# of dir(), when user defined objects are
# passed are parameters.


# Creation of a simple class with __dir()__
# method to demonstrate it's working
class Supermarket:

    # Function __dir()___ which list all
    # the base attributes to be used.
    def __dir__(self):
        return['customer_name', 'product',
               'quantity', 'price', 'date']


# user-defined object of class supermarket
my_cart = Supermarket()

# listing out the dir() method
print(dir(my_cart))

Output :

['customer_name', 'date', 'price', 'product', 'quantity']

Applications :

• The dir() has it’s own set of uses. It is usually used for debugging purposes in simple day to day programs, and even in large projects taken up by a team of developers. The capability of dir() to list out all the attributes of the parameter passed, is really useful when handling a lot of classes and functions, separately. 
  
• The dir() function can also list out all the available attributes for a module/list/dictionary. So, it also gives us information on the operations we can perform with the available list or module, which can be very useful when having little to no information about the module. It also helps to know new modules faster.