The difference between is and == from the three elements of Python objects The difference between is and == from the three elements of Python objects

The difference between is and == from the three elements of Python objects

July 06, 2017 17:01:34

Number of readings: 412

Three elements of Python object

Python objects contain three basic elements id, type and value:

element	illustrate	method of obtaining
id	Identity, basically a memory address	id(obj)
type	type of data	type(obj)
value	value

The difference between is and ==

logo	name	Judgment factor
is	identity operator	id
==	comparison operator	value

Example

Example 1

a = {"a":1, "b":2}
b = a.copy()

a == b  # True value一样
a is b  # False id不一样

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Example 2

>>> x = y = [4,5,6]
>>> z = [4,5,6]
>>> x == y
True
>>> x == z
True
>>> x is y
True
>>> x is z
False
>>>
>>> print id(x)
>>> print id(y)
>>> print id(z)

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Example 3

>>> a = 1 #a和b为数值类型
>>> b = 1
>>> a is b
True
>>> id(a)
>>> id(b)
>>> a = 'cheesezh' #a和b为字符串类型
>>> b = 'cheesezh'
>>> a is b
True
>>> id(a)
>>> id(b)
>>> a = (1,2,3) #a和b为元组类型
>>> b = (1,2,3)
>>> a is b
False
>>> id(a)
>>> id(b)
>>> a = [1,2,3] #a和b为list类型
>>> b = [1,2,3]
>>> a is b
False
>>> id(a)
>>> id(b)
>>> a = {'cheese':1,'zh':2} #a和b为dict类型
>>> b = {'cheese':1,'zh':2}
>>> a is b
False
>>> id(a)
>>> id(b)
>>> a = set([1,2,3])#a和b为set类型
>>> b = set([1,2,3])
>>> a is b
False
>>> id(a)
>>> id(b)

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It can be seen from Example 3 that a is b is True only in the case of numeric and string types, and a is b is False when a and b are tuple, list, dict or set types.

refer to

• Objects, values and types
• Value comparisons
• Difference between is and == in Python

Copyright statement: This article is an original article by blogger  lilongs y, welcome to reprint, please indicate the original source of the article in the form of a hyperlink when reprinting. https://blog.csdn.net/lilongsy/article/details/74570542