Identity Type Value¶

Three Characteristics¶

x = [1, 2, 3]

print(id(x))        # Identity
print(type(x))      # Type
print(x)            # Value

a = [1, 2, 3]
b = [1, 2, 3]

print(id(a) != id(b))  # True

CPython note: id() returns the memory address:

x = [1, 2, 3]
print(id(x))       # e.g., 140234567890
print(hex(id(x)))  # e.g., '0x7f8b2c3d4e50'

Other implementations (PyPy, Jython) may return a different unique token.

x = [1, 2, 3]
original_id = id(x)

x.append(4)
print(id(x) == original_id)  # True

a = [1, 2, 3]
b = a
c = [1, 2, 3]

print(a is b)       # True
print(a is c)       # False

x = 42
y = "42"

print(type(x))      # <class 'int'>
print(type(y))      # <class 'str'>

x = [1, 2, 3]
# Cannot change type

x = [1, 2, 3]
print(x)            # [1, 2, 3]

x = [1, 2, 3]
x[0] = 100
print(x)            # [100, 2, 3]