Python3標識運算符實例
Python 內置函數 id() 返回一個唯一的整數作爲對象的身份。標識運算符比較兩個對象的存儲單元。Python有兩個標識操作符如下面所解釋:
操作符
描述
示例
is
如果操作符兩側的變量是相同的對象計算結果爲true,否則返回 false
x is y,如果 id(x) 等於 id(y) ,則結果爲1
is not
如果操作符兩側的變量不是相同的對象計算結果爲true,否則返回 false
x is y,如果 id(x) 不等於 id(y) ,則結果爲1
示例
#!/usr/bin/python3
a = 20
b = 20
print ('Line 1','a=',a,':',id(a), 'b=',b,':',id(b))
if ( a is b ):
print ("Line 2 - a and b have same identity")
else:
print ("Line 2 - a and b do not have same identity")
if ( id(a) == id(b) ):
print ("Line 3 - a and b have same identity")
else:
print ("Line 3 - a and b do not have same identity")
b = 30
print ('Line 4','a=',a,':',id(a), 'b=',b,':',id(b))
if ( a is not b ):
print ("Line 5 - a and b do not have same identity")
else:
print ("Line 5 - a and b have same identity")
當你執行上面的程序它產生以下結果 -
Line 1 a= 20 : 1594701888 b= 20 : 1594701888
Line 2 - a and b have same identity
Line 3 - a and b have same identity
Line 4 a= 20 : 1594701888 b= 30 : 1594702048
Line 5 - a and b do not have same identity