future 模块
python 3.x引进了一些python2.7.x不兼容的关键字和功能,所以我们可以通过在python 2中导入future模型进行使用python3的特性.
如果我们想在python 2中使用python 3的整除,那么就可以导入下列: from __future__ import division
future模块的另外一些功能
print 函数
python 2
print 'Python', python_version()
print 'Hello, World!'
print(
'Hello, World!')
print "text", ;
print 'print more text on the same line'
Python
2.7.6
Hello, World!
Hello, World!
text print more
text on the same line
python 3
print(
'Python', python_version())
print(
'Hello, World!')
print(
"some text,",
end=
"") ##notice:不换行的方式.
print(
' print more text on the same line')
Python
3.4.1
Hello, World!
some text, print more
text on the same line
整数除法
特别注意的地方是在将python2代码移植到python 3的时候,整数除法是不会引起任何报错信息的,但它却会改变数值的精度. 所以在python 2使用除法时,建议使用future模块的division.
python 2
print 'Python', python_version()
print '3 / 2 =',
3 /
2
print '3 // 2 =',
3
print '3 / 2.0 =',
3 /
2.0
print '3 // 2.0 =',
3
Python
2.7.6
3 /
2 =
1
3
3 /
2.0 =
1.5
3
python 3
print(
'Python', python_version())
print(
'3 / 2 =',
3 /
2)
print(
'3 // 2 =',
3
print(
'3 / 2.0 =',
3 /
2.0)
print(
'3 // 2.0 =',
3
Python
3.4.1
3 /
2 =
1.5
3
3 /
2.0 =
1.5
3
Unicode
python 2 没有byte类型,而python 3中,我们有Unicode(utf-8) str, 和两种byte类型:byte和bytearray.
python 2
print type(unicode(
'this is like a python3 str type'))
print type(
b'byte type does not exist')
print 'they are really' +
b' the same'
print type(bytearray(
b'bytearray oddly does exist though'))
<
type 'unicode'>
<
type 'str'>
they are really the same
<
type 'bytearray'>
python 3
print(
'Python', python_version())
print(
'strings are now utf-8 \u03BCnico\u0394é!')
print(
'Python', python_version())
print(
'strings are now utf-8 \u03BCnico\u0394é!')
print(
'and Python', python_version(),
end=
"")
print(
' also has',
type(bytearray(b
'bytearrays')))
'note that we cannot add a string' + b
'bytes for data'
Python
3.4.
1
strings are now utf-
8 μnicoΔé!
Python
3.4.
1 has <
class 'bytes'>
and Python
3.4.
1 also
has <
class 'bytearray'>
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-
13-d3e8942ccf81>
in <
module>()
---->
1 'note that we cannot add a string' + b
'bytes for data'
TypeError: Can
't convert 'bytes
' object to str implicitly
xrange
使用%timeit + func 的形式来测试该函数测运行效率.注意最好在ipython环境下使用%timeit.
python 2
In [
3]: def test_range(n):
...:
for i
in range(n):
...: pass
...:
In [
4]: def test_xrange(n):
...:
for i
in xrange(n):
...: pass
...:
In [
6]: %timeit test_range(
1000)
100000 loops, best
of 3:
15.4 µs per
loop
In [
7]: %timeit test_xrange(
1000)
The slowest run took
10.07 times longer than the fastest. This could mean that an intermediate
result is being cached.
100000 loops, best
of 3:
10.7 µs per
loop
python 3
而python 3只有range(),并没有xrange()
print('Python', python_version())
print('\ntiming range()')
%timeit
test_range(n)
print(xrange(10))
Python 3.4.1
timing range()
1000 loops, best of 3: 520 µs per loop
NameError Traceback (most recent
call last)
<ipython-input-5-5d8f9b79ea70> in <module>()
----> 1 print(xrange(10))
NameError: name 'xrange' is not defined
contains method for range objects in python 3
Raising exceptions
python 2
python 3
Handling exceptions
python 2
python 3
next() 和.next()
python 2
python 3
For-loop 和global namespace leak
python 2
python 3
比较无顺序的类型
python 2
python 3
python 2
python 3
返回迭代对象
python 2
python 3
round
参考链接:
http://sebastianraschka.com/Articles/2014_python_2_3_key_diff.html
