Python id() Function
Python3 Built-in Functionsid()It is a built-in function in Python used to obtain the unique identifier of an object.
In Python, each object has a unique integer identifier, which is unique and constant throughout the object's lifetime.id()It returns this identifier, which usually corresponds to the object's memory address.
Word Definition： idYesidentifierAbbreviation for (identifier).
Basic Syntax and Parameters
Syntax Format
id(object)
Parameter Description
- Parameter object：
- Type: Any object
- Description: The object whose identifier is to be obtained.
Function Description
- Return Value: Returns an integer representing the object's unique identifier.
- Characteristics: The id remains constant throughout the object's lifetime.
Examples
Example 1: Basic Usage
Example
# View the id of an integer
a = 10
print(id(a)) # Output: an integer, e.g., 4302400000
# View the id of a string
s = "hello"
print(id(s)) # Output: an integer
# View the id of a list
lst = [1, 2, 3]
print(id(lst)) # Output: an integer
a = 10
print(id(a)) # Output: an integer, e.g., 4302400000
# View the id of a string
s = "hello"
print(id(s)) # Output: an integer
# View the id of a list
lst = [1, 2, 3]
print(id(lst)) # Output: an integer
Expected Output:
Returns the object's unique identifier (an integer).
Code Analysis:
- Every object has a unique id.
- Different objects usually have different ids.
Example 2: Verify Object Identity
Example
# Same object referenced multiple times
a = [1, 2, 3]
b = a
print(id(a) == id(b)) # Output: True (a and b point to the same object)
# Copy an object
a = [1, 2, 3]
b = a.copy()
print(id(a) == id(b)) # Output: False (a and b are different objects)
# Integer caching (small integers)
a = 256
b = 256
print(id(a) == id(b)) # Output: True (small integers are cached)
a = 257
b = 257
print(id(a) == id(b)) # Output: False (large integers are not cached)
a = [1, 2, 3]
b = a
print(id(a) == id(b)) # Output: True (a and b point to the same object)
# Copy an object
a = [1, 2, 3]
b = a.copy()
print(id(a) == id(b)) # Output: False (a and b are different objects)
# Integer caching (small integers)
a = 256
b = 256
print(id(a) == id(b)) # Output: True (small integers are cached)
a = 257
b = 257
print(id(a) == id(b)) # Output: False (large integers are not cached)
Expected Output:
True False True False
Code Analysis:
- Use
==Comparing ids can determine whether they are the same object. - Python caches small integers (-5 to 256), so variables with the same value may share the same id.
Example 3: Practical Application
Example
# Check whether it is the same object
def check_same_object(a, b):
return id(a) == id(b)
# Test
list1 = [1, 2, 3]
list2 = list1
list3 = [1, 2, 3]
print(check_same_object(list1, list2)) # Output: True
print(check_same_object(list1, list3)) # Output: False
# Use as a dictionary key (though not common)
d = {}
obj = object()
d[obj] = "value"
print(d[obj]) # Output: value
# View objects during debugging
class Person:
pass
p = Person()
print(f"Object id: {id(p)}")
print(f"Class id: {id(Person)}")
def check_same_object(a, b):
return id(a) == id(b)
# Test
list1 = [1, 2, 3]
list2 = list1
list3 = [1, 2, 3]
print(check_same_object(list1, list2)) # Output: True
print(check_same_object(list1, list3)) # Output: False
# Use as a dictionary key (though not common)
d = {}
obj = object()
d[obj] = "value"
print(d[obj]) # Output: value
# View objects during debugging
class Person:
pass
p = Person()
print(f"Object id: {id(p)}")
print(f"Class id: {id(Person)}")
Expected Output:
True False value 对象 id: ... 类 id: ...
id()Mainly used for debugging, checking object identity, understanding Python memory management, and other aspects.
Other Extensions