1 使用 __future__的模块

python3.x 引入了一些与python2.x不兼容的关键字和特性。2.x中可以通过__future__模块导入新的内容

2 print函数

2.x中print是个语句，3.x中print是个方法，也是说2.x中print 或者print() 、print () 都是可以的，

print "magedu.com" print("magedu.com") print ("magedu.com")

不过3.x中print一定要方法的形式调用

print("magedu.com")

3 整数除法

python2.x

>>> 1/2 0

python3.x

>>> 1/2 0.5 >>> 1/0

4 Unicode

python2.x：ASCII的str类型，有unicode() 转成unicode类型 Python 2.7.16 (default, Apr 17 2020, 18:29:03) [GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.29.20) (-macos10.15-objc- on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import sys >>> sys.getdefaultencoding() 'ascii' python3.x：Unicode(utf-8)类型str，bytes，bytearrays Python 3.7.3 (default, Mar 7 2020, 00:16:22) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import sys >>> sys.getdefaultencoding() 'utf-8' >>>

5 xrange

python2.x xrangepython3.x range，使用xrange会有异常

6 异常

python2.x 支持两种格式 Python 2.7.16 (default, Apr 17 2020, 18:29:03) [GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.29.20) (-macos10.15-objc- on darwin Type "help", "copyright", "credits" or "license" for more information. >>> try: ... a = raw_input("输入一个数：") ... if not a.isdigit(): ... raise ValueError("a 必须是数字") ... except ValueError as e: ... print("引发异常：",e) ... 输入一个数：a ('\xe5\xbc\x95\xe5\x8f\x91\xe5\xbc\x82\xe5\xb8\xb8\xef\xbc\x9a', ValueError('a \xe5\xbf\x85\xe9\xa1\xbb\xe6\x98\xaf\xe6\x95\xb0\xe5\xad\x97',)) >>> try: ... a = raw_input("输入一个数：") ... if not a.isdigit(): ... raise ValueError("a 必须是数字") ... except ValueError,e: ... print("引发异常：",e) ... 输入一个数：a ('\xe5\xbc\x95\xe5\x8f\x91\xe5\xbc\x82\xe5\xb8\xb8\xef\xbc\x9a', ValueError('a \xe5\xbf\x85\xe9\xa1\xbb\xe6\x98\xaf\xe6\x95\xb0\xe5\xad\x97',)) python3.x 只支持as e的这种 Python 3.7.3 (default, Mar 7 2020, 00:16:22) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> try: ... a = input("输入一个数：") ... if not a.isdigit(): ... raise ValueError("a 必须是数字") ... except ValueError as e: ... print("引发异常：",e) ... 输入一个数：a 引发异常： a 必须是数字 >>>

7 next方法

python2.x next() 或者.next()python3.x next() __next__

8 input方法

python2.x raw_input()python3.x input()

9 iter和list

python2.x 有些迭代对象直接转成list了:dict.key(),dict.values(), map, reduce,filter等等 Python 2.7.16 (default, Apr 17 2020, 18:29:03) [GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.29.20) (-macos10.15-objc- on darwin Type "help", "copyright", "credits" or "license" for more information. >>> lst = map(lambda x:int(x), [x for x in "123456789"]) >>> type(lst) <type 'list'> >>> lst [1, 2, 3, 4, 5, 6, 7, 8, 9] >>> dt = {x:x for x in range(10)} >>> dt.values() dict_values([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]) >>> dt.keys() dict_keys([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]) >>> dt.items() dict_items([(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6), (7, 7), (8, 8), (9, 9)]) >>> python3.x 默认返回的是可迭代对象:dict.key(),dict.values(), map, reduce,filter等等 Python 3.7.3 (default, Mar 7 2020, 00:16:22) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> lst = map(lambda x:int(x), [x for x in "123456789"]) >>> type(lst) <class 'map'> >>> lst <map object at 0x10457a128> >>> >>> dt = {x:x for x in range(10)} >>> dt.values() dict_values([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]) >>> dt.keys() dict_keys([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]) >>> dt.items() dict_items([(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6), (7, 7), (8, 8), (9, 9)]) >>>

10 字典

python2.x 字典插入无序 Python 2.7.16 (default, Apr 17 2020, 18:29:03) [GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.29.20) (-macos10.15-objc- on darwin Type "help", "copyright", "credits" or "license" for more information. >>> dt = {} >>> dt["a"] = "A" >>> dt["b"] = "B" >>> dt["c"] = "C" >>> dt {'a': 'A', 'c': 'C', 'b': 'B'} >>> python3.5以后，字典插入有序 >>> dt = {} >>> dt["a"] = "A" >>> dt["b"] = "B" >>> dt["c"] = "C" >>> dt {'a': 'A', 'b': 'B', 'c': 'C'} >>>

11 字符串格式化

python2.x % >>> a = "%d+%d=%d" %(1,2,3) >>> a '1+2=3' python3.x format 和f Python 3.7.3 (default, Mar 7 2020, 00:16:22) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> a = "{}+{}={}".format(1,2,3) >>> a '1+2=3' >>> a = 1 >>> b = 2 >>> c = 3 >>> d = f"{a}+{b}={c}" >>> d '1+2=3'

12 True和False

python2.x True 可以被赋值 Python 2.7.16 (default, Apr 17 2020, 18:29:03) [GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.29.20) (-macos10.15-objc- on darwin Type "help", "copyright", "credits" or "license" for more information. >>> True + True 2 >>> True = 0 >>> True + True 0 >>> python3.x True是关键字 Python 3.7.3 (default, Mar 7 2020, 00:16:22) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> True+True 2 >>> True = 0 File "<stdin>", line 1 SyntaxError: can't assign to keyword >>>

python2.x 里面 while 1 要比while True 速度快一些(来自你像从前一样的Python学习笔记-python天坑系列)

➜ Desktop cat python2.py #! /usr/bin/python # -*- coding: utf-8 -*- import timeit def while_one(): i = 0 while 1: i += 1 if i == 10000000: break def while_true(): i = 0 while True: i += 1 if i == 10000000: break if __name__ == "__main__": w1 = timeit.timeit(while_one, "from __main__ import while_one", number=3) wt = timeit.timeit(while_true, "from __main__ import while_true", number=3) print "while one: %s\nwhile_true: %s" % (w1, wt) ➜ Desktop python python2.py while one: 0.646219015121 while_true: 1.01446509361

欢迎小伙伴来补充