Python setattr() Function
Python3 Built-in Functionssetattr()is a built-in function in Python used to set object attributes.
Unlike directly using dot (.) notation for assignment,setattr()it allows you to dynamically set object attributes through strings. This is very useful when you need to set attributes based on variable names or handle unknown attributes.
Word Definition： setattrYesset attributeabbreviation for "set attribute".
Basic Syntax and Parameters
Syntax Format
setattr(obj, name, value)
Parameter Description
- Parameter obj：
- Type: Any object
- Description: The object whose attribute is to be set.
- Parameter name：
- Type: String
- Description: The name of the attribute to set (in string form).
- Parameter value：
- Type: Any value
- Description: The value to set.
Function Description
- Return value: No return value (returns
None）。 - Corresponding function: Used with
getattr()together with the function,getattrused to get attributes.
Examples
Example 1: Basic Usage
Example
# Create a simple class
class Person:
pass
# Create an object
p = Person()
# Use setattr to set attributes
setattr(p, 'name', 'Tom')
setattr(p, 'age', 20)
setattr(p, 'city', 'Beijing')
# Verify the attribute has been set
print(p.name) # Output: Tom
print(p.age) # Output: 20
print(p.city) # Output: Beijing
# Use getattr to get attributes
print(getattr(p, 'name')) # Output: Tom
class Person:
pass
# Create an object
p = Person()
# Use setattr to set attributes
setattr(p, 'name', 'Tom')
setattr(p, 'age', 20)
setattr(p, 'city', 'Beijing')
# Verify the attribute has been set
print(p.name) # Output: Tom
print(p.age) # Output: 20
print(p.city) # Output: Beijing
# Use getattr to get attributes
print(getattr(p, 'name')) # Output: Tom
Expected Output:
Tom 20 Beijing Tom
Code Analysis:
setattr(obj, 'name', 'Tom')Equivalent toobj.name = 'Tom'。- The attribute name is passed as a string, allowing dynamic setting.
- Can be used with
getattr()together.
Example 2: Dynamically Setting Attributes
Example
class Student:
pass
# Dynamically set multiple attributes
student = Student()
fields = ['name', 'age', 'grade', 'school']
values = ['Lily', 18, 'A', 'MIT']
for field, value in zip(fields, values):
setattr(student, field, value)
# Print all attributes
for field in fields:
print(f"{field}: {getattr(student, field)}")
# Set a non-existent attribute
setattr(student, 'major', 'Computer Science')
print(student.major) # Output: Computer Science
pass
# Dynamically set multiple attributes
student = Student()
fields = ['name', 'age', 'grade', 'school']
values = ['Lily', 18, 'A', 'MIT']
for field, value in zip(fields, values):
setattr(student, field, value)
# Print all attributes
for field in fields:
print(f"{field}: {getattr(student, field)}")
# Set a non-existent attribute
setattr(student, 'major', 'Computer Science')
print(student.major) # Output: Computer Science
Expected Output:
name: Lily age: 18 grade: A school: MIT Computer Science
Code Analysis:
- Multiple attributes can be set dynamically through a loop.
- setattr can add new attributes to an object.
- This is useful when handling configuration files or user input.
Example 3: Working with __dict__
Example
# View the object's __dict__
class Car:
def __init__(self):
self.brand = "Toyota"
car = Car()
print(car.__dict__) # Output: {'brand': 'Toyota'}
# Use setattr to add attributes
setattr(car, 'model', 'Camry')
setattr(car, 'year', 2024)
print(car.__dict__) # Output: {'brand': 'Toyota', 'model': 'Camry', 'year': 2024}
# Check if the attribute exists
if hasattr(car, 'brand'):
print(f"Brand: {getattr(car, 'brand')}")
class Car:
def __init__(self):
self.brand = "Toyota"
car = Car()
print(car.__dict__) # Output: {'brand': 'Toyota'}
# Use setattr to add attributes
setattr(car, 'model', 'Camry')
setattr(car, 'year', 2024)
print(car.__dict__) # Output: {'brand': 'Toyota', 'model': 'Camry', 'year': 2024}
# Check if the attribute exists
if hasattr(car, 'brand'):
print(f"Brand: {getattr(car, 'brand')}")
Expected Output:
{'brand': 'Toyota'}
{'brand': 'Toyota', 'model': 'Camry', 'year': 2024}
品牌: Toyota
setattr()Usually used withgetattr()、hasattr()、delattr()together, forming a complete toolset for attribute operations.
Other Extensions