[Python知识库]python2与python3的区别

1.输出差异

python2:
>>> print "ok"
ok
>>> print ("ok")
ok
>>>

python3:
>>> print("ok")
ok
>>> print "ok"
  File "<stdin>", line 1
    print "ok"
             ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print("ok")?
>>>

2.输入差异

python2:
>>> num1 = input("please input your number")
please input your number12
>>> type(num1)
<type 'int'>
>>> num1 = input("please input your number")
please input your number"abc"
>>> type(num1)
<type 'str'>
>>> num1 = raw_input("please input your number")
please input your number12
>>> type(num1)
<type 'str'>
>>>

3.数据类型差异

python2:
>>> type(10000000000000000000000000000000)
<type 'long'>
>>>

python3:
>>> type(100000000000000000000000000)
<class 'int'>
>>>

4.运算符差异

python2:
>>> 3/5
0
>>> 6/4
1
>>> 6.0/4
1.5
>>>

python3:
>>> 3/5
0.6
>>> 6/4
1.5
>>> 3//5
0
>>> 6//4
1
>>>

5.比较运算

>>> 6 <> 5
True
>>> 6 != 5
True
>>>


python3:
>>> 6 <> 5
  File "<stdin>", line 1
    6 <> 5
       ^
SyntaxError: invalid syntax
>>> 6 != 5
True
>>>

6.range的差异

python2:
>>> range(10)       #直接返回一个列表，存在内存里
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> xrange(10)      #生成一个可迭代对象，用的时候才生成到内存里，用完就释放内存
xrange(10)
>>>

python3:
>>> range(10)   #生成一个可迭代对象，和python2的xrange一样
range(0, 10)
>>>

7.异常机制的差异

python2:
except IndexError , ie:
python3:
except IndexError as ie:

8.编码的差异

python2编码:ascii码
python3编码:utf-8

9.布尔类型的差异

python2:True和False不是关键字，可以作为变量名
python3:True和False是关键字，不可以作为变量名