Python 2.7.x와 3.x 버전 간의 중요한 차이점

from platform import python_version

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

print('Python', python_version())
print('Hello, World!')
 
print("some text,", end="") 
print(' print more text on the same line')

Python 3.4.1
Hello, World!
some text, print more text on the same line

print 'Hello, World!'

File "", line 1
print 'Hello, World!'
^
SyntaxError: invalid syntax

print 'Python', python_version()
print('a', 'b')
print 'a', 'b'

Python 2.7.7
('a', 'b')
a b

print 'Python', python_version()
print '3 / 2 =', 3 / 2
print '3 // 2 =', 3 // 2
print '3 / 2.0 =', 3 / 2.0
print '3 // 2.0 =', 3 // 2.0

Python 2.7.6
3 / 2 = 1
3 // 2 = 1
3 / 2.0 = 1.5
3 // 2.0 = 1.0

print('Python', python_version())
print('3 / 2 =', 3 / 2)
print('3 // 2 =', 3 // 2)
print('3 / 2.0 =', 3 / 2.0)
print('3 // 2.0 =', 3 // 2.0)

Python 3.4.1
3 / 2 = 1.5
3 // 2 = 1
3 / 2.0 = 1.5
3 // 2.0 = 1.0

print type(unicode('this is like a python3 str type'))

<type &#39;unicode&#39;>

print type(b'byte type does not exist')

<type &#39;str&#39;>

print 'they are really' + b' the same'

they are really the same

print type(bytearray(b'bytearray oddly does exist though'))

<type &#39;bytearray&#39;>

print('Python', python_version())
print('strings are now utf-8 u03BCnicou0394é!')

Python 3.4.1
strings are now utf-8 μnicoΔé!

print('Python', python_version(), end="")
print(' has', type(b' bytes for storing data'))

Python 3.4.1 has <class &#39;bytes&#39;>

print('and Python', python_version(), end="")
print(' also has', type(bytearray(b'bytearrays')))

and Python 3.4.1 also has <class &#39;bytearray&#39;>

'note that we cannot add a string' + b'bytes for data'

---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
 in ()
----> 1 'note that we cannot add a string' + b'bytes for data'
 
TypeError: Can't convert 'bytes' object to str implicitly

import timeit
 
n = 10000
def test_range(n):
 return for i in range(n):
 pass
 
def test_xrange(n):
 for i in xrange(n):
 pass

print 'Python', python_version()
 
print 'ntiming range()'
%timeit test_range(n)
 
print 'nntiming xrange()'
%timeit test_xrange(n)

Python 2.7.6
 
timing range()
1000 loops, best of 3: 433 µs per loop
 
timing xrange()
1000 loops, best of 3: 350 µs per loop

print('Python', python_version())
 
print('ntiming range()')
%timeit test_range(n)

Python 3.4.1
 
timing range()
1000 loops, best of 3: 520 µs per loop

print(xrange(10))

---------------------------------------------------------------------------
NameError Traceback (most recent call last)
in ()
----> 1 print(xrange(10))
 
NameError: name 'xrange' is not defined

x = 10000000
def val_in_range(x, val):
 return val in range(x)
 
def val_in_xrange(x, val):
 return val in xrange(x)
 
print('Python', python_version())
assert(val_in_range(x, x/2) == True)
assert(val_in_range(x, x//2) == True)
%timeit val_in_range(x, x/2)
%timeit val_in_range(x, x//2)

Python 3.4.1
1 loops, best of 3: 742 ms per loop
1000000 loops, best of 3: 1.19 µs per loop

print 'Python', python_version()
 
assert(val_in_xrange(x, x/2.0) == True)
assert(val_in_xrange(x, x/2) == True)
assert(val_in_range(x, x/2) == True)
assert(val_in_range(x, x//2) == True)
%timeit val_in_xrange(x, x/2.0)
%timeit val_in_xrange(x, x/2)
%timeit val_in_range(x, x/2.0)
%timeit val_in_range(x, x/2)

Python 2.7.7
1 loops, best of 3: 285 ms per loop
1 loops, best of 3: 179 ms per loop
1 loops, best of 3: 658 ms per loop
1 loops, best of 3: 556 ms per loop

Python 3.4.1
<slot wrapper &#39;__contains__&#39; of &#39;range&#39; objects

Python 2.7.7
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
 in ()
1 print 'Python', python_version()
----> 2 range.__contains__
 
AttributeError: 'builtin_function_or_method' object has no attribute '__contains__'

print('Python', python_version())
xrange.__contains__

Python 2.7.7
 
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
in ()
1 print 'Python', python_version()
----> 2 xrange.__contains__
 
AttributeError: type object 'xrange' has no attribute '__contains__'

def test_while():
 i = 0
 while i < 20000:
  i += 1
 return

print('Python', python_version())
%timeit test_while()

Python 3.4.1
%timeit test_while()
100 loops, best of 3: 2.68 ms per loop

print 'Python', python_version()
%timeit test_while()

Python 2.7.6
1000 loops, best of 3: 1.72 ms per loop

---------------------------------------------------------------------------
IOError Traceback (most recent call last)
 in ()
----> 1 raise IOError, "file error"
 
IOError: file error

raise IOError("file error")

---------------------------------------------------------------------------
IOError Traceback (most recent call last)
 in ()
----> 1 raise IOError("file error")
 
IOError: file error

print('Python', python_version())

Python 3.4.1

File "", line 1
raise IOError, "file error"
^
SyntaxError: invalid syntax
The proper way to raise an exception in Python 3:

print('Python', python_version())
raise IOError("file error")

Python 3.4.1
 
---------------------------------------------------------------------------
OSError Traceback (most recent call last)
 in ()
1 print('Python', python_version())
----> 2 raise IOError("file error")
 
OSError: file error

print 'Python', python_version()
try:
 let_us_cause_a_NameError
except NameError, err:
 print err, '--> our error message'

Python 2.7.6
name 'let_us_cause_a_NameError' is not defined --> our error message

print('Python', python_version())
try:
 let_us_cause_a_NameError
except NameError as err:
 print(err, '--> our error message')

Python 3.4.1
name 'let_us_cause_a_NameError' is not defined --> our error message

print 'Python', python_version()
my_generator = (letter for letter in 'abcdefg')
next(my_generator)
my_generator.next()

Python 2.7.6
'b'

print('Python', python_version())
my_generator = (letter for letter in 'abcdefg')
next(my_generator)

Python 3.4.1
'a'

my_generator.next()

---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-14-125f388bb61b> in <module>()
----> 1 my_generator.next()
 
AttributeError: &#39;generator&#39; object has no attribute &#39;next&#39;

print 'Python', python_version()
 
i = 1
print 'before: i =', i
 
print 'comprehension: ', [i for i in range(5)]
 
print 'after: i =', i

Python 2.7.6
before: i = 1
comprehension: [0, 1, 2, 3, 4]
after: i = 4

print('Python', python_version())
 
i = 1
print('before: i =', i)
 
print('comprehension:', [i for i in range(5)])
 
print('after: i =', i)

Python 3.4.1
before: i = 1
comprehension: [0, 1, 2, 3, 4]
after: i = 1

print 'Python', python_version()
print "[1, 2] > 'foo' = ", [1, 2] > 'foo'
print "(1, 2) > 'foo' = ", (1, 2) > 'foo'
print "[1, 2] > (1, 2) = ", [1, 2] > (1, 2)

Python 2.7.6
[1, 2] > 'foo' = False
(1, 2) > 'foo' = True
[1, 2] > (1, 2) = False

print('Python', python_version())
print("[1, 2] > 'foo' = ", [1, 2] > 'foo')
print("(1, 2) > 'foo' = ", (1, 2) > 'foo')
print("[1, 2] > (1, 2) = ", [1, 2] > (1, 2))

Python 3.4.1
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
 in ()
1 print('Python', python_version())
----> 2 print("[1, 2] > 'foo' = ", [1, 2] > 'foo')
3 print("(1, 2) > 'foo' = ", (1, 2) > 'foo')
4 print("[1, 2] > (1, 2) = ", [1, 2] > (1, 2))
TypeError: unorderable types: list() > str()

Python 2.7.6
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
 
>>> my_input = input('enter a number: ')
 
enter a number: 123
 
>>> type(my_input)

 
>>> my_input = raw_input('enter a number: ')
 
enter a number: 123
 
>>> type(my_input)
<type &#39;str&#39;>

Python 3.4.1
[GCC 4.2.1 (Apple Inc. build 5577)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
 
>>> my_input = input('enter a number: ')
enter a number: 123
>>> type(my_input)
<class &#39;str&#39;>

print 'Python', python_version()
 
print range(3)
print type(range(3))

Python 2.7.6
[0, 1, 2]
<type &#39;list&#39;>

print('Python', python_version())
print(range(3))
print(type(range(3)))
print(list(range(3)))

Python 3.4.1
range(0, 3)
<class &#39;range&#39;>
[0, 1, 2]