Python dir() Function
Python3 Built-in Functionsdir()It is a built-in function in Python used to obtain a list of object attributes and methods.
dir()Returns a list containing the names of all attributes and methods of the object. This function is very useful for exploring unknown objects, debugging code, and understanding class structures.
Word Definition： dirYesdirectoryAbbreviation of (directory), here referring to the list of attributes and methods.
Basic Syntax and Parameters
Syntax Format
dir(object) dir()
Parameter Description
- Parameter object(Optional):
- Type: Any object
- Description: The object whose attribute list you want to obtain. If no parameter is passed, it returns the list of names in the current scope.
Function Description
- Return Value: Returns a list of strings containing the names of attributes and methods.
- Features: The list is sorted alphabetically.
Examples
Example 1: View Object Attributes
Example
# View all attributes and methods of a list
print(dir([]))
# Output: ['__add__', '__class__', '__contains__', ... 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
# View attributes of a string
print(dir(""))
# Output: ['__add__', '__class__', '__contains__', ... 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
# View attributes of a dictionary
print(dir({}))
# Output: ['__class__', '__contains__', ... 'clear', 'copy', 'get', 'items', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']
print(dir([]))
# Output: ['__add__', '__class__', '__contains__', ... 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
# View attributes of a string
print(dir(""))
# Output: ['__add__', '__class__', '__contains__', ... 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
# View attributes of a dictionary
print(dir({}))
# Output: ['__class__', '__contains__', ... 'clear', 'copy', 'get', 'items', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']
Expected Output:
Returns a list of all attribute and method names of the object.
Code Explanation:
- Starting with double underscore
__are special attributes/methods (magic methods). - Those without double underscores are public methods, such as
append,sortetc.
Example 2: View Custom Class Attributes
Example
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def greet(self):
return f"Hello, I'm {self.name}"
# Create instance
p = Person("Tom", 20)
# View instance attributes
print(dir(p))
# Output: ['__class__', '__delattr__', '__dict__', '__init__', ... 'age', 'greet', 'name']
# Filter to show only non-special methods
attrs = [attr for attr in dir(p) if not attr.startswith('_')]
print(attrs) # Output: ['age', 'greet', 'name']
def __init__(self, name, age):
self.name = name
self.age = age
def greet(self):
return f"Hello, I'm {self.name}"
# Create instance
p = Person("Tom", 20)
# View instance attributes
print(dir(p))
# Output: ['__class__', '__delattr__', '__dict__', '__init__', ... 'age', 'greet', 'name']
# Filter to show only non-special methods
attrs = [attr for attr in dir(p) if not attr.startswith('_')]
print(attrs) # Output: ['age', 'greet', 'name']
Expected Output:
['__class__', '__delattr__', '__dict__', '__init__', ... 'age', 'greet', 'name'] ['age', 'greet', 'name']
Code Explanation:
__dict__Contains the instance attributes of the object.- Filter
__out methods starting with (double underscores) to get public attributes.
Example 3: Using Without Parameters
Example
# Without parameters, returns the list of names in current scope
print(dir())
# Output: ['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__']
# View after importing module
import os
print(dir())
# Will include 'os' in the list
# View module attributes
import json
print(dir(json))
# Output: ['JSONDecodeError', '__all__', '__author__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'decoder', 'dump', 'dumps', 'encoder', 'load', 'loads', 'tool']
print(dir())
# Output: ['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__']
# View after importing module
import os
print(dir())
# Will include 'os' in the list
# View module attributes
import json
print(dir(json))
# Output: ['JSONDecodeError', '__all__', '__author__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'decoder', 'dump', 'dumps', 'encoder', 'load', 'loads', 'tool']
Expected Output:
Returns the list of names available in the current scope.
dir()It is a powerful tool for exploring Python objects and modules, especially suitable for interactive learning and debugging.
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