Python：あなたが知らないかもしれないこと

>>> a = [1, 2, 3, 4] >>> a.append(a) >>> a [1, 2, 3, 4, [...]] >>> a[4] [1, 2, 3, 4, [...]] >>> a[4][4][4][4][4][4][4][4][4][4] == a True 

 >>> a = {} >>> b = {} >>> a['b'] = b >>> b['a'] = a >>> print a {'b': {'a': {...}}} 

 >>> l = [[1, 2, 3], [4, 5], [6], [7, 8, 9]] >>> sum(l, []) [1, 2, 3, 4, 5, 6, 7, 8, 9] 

 [y for x in data for y in x] 

 import itertools data = [[1, 2, 3], [4, 5, 6]] list(itertools.chain.from_iterable(data)) 

 from functools import reduce from operator import add data = [[1, 2, 3], [4, 5, 6]] reduce(add, data) 

 >>> {a:a**2 for a in range(1, 10)} {1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81} 

 class foo: def normal_call(self): print("normal_call") def call(self): print("first_call") self.call = self.normal_call 

 >>> y = foo() >>> y.call() first_call >>> y.call() normal_call >>> y.call() normal_call 

 class GetAttr(object): def __getattribute__(self, name): f = lambda: "Hello {}".format(name) return f 

 >>> g = GetAttr() >>> g.Mark() 'Hello Mark' 

 >>> a = set([1,2,3,4]) >>> b = set([3,4,5,6]) >>> a | b #  {1, 2, 3, 4, 5, 6} >>> a & b #  {3, 4} >>> a < b #  False >>> a - b #  {1, 2} >>> a ^ b #   {1, 2, 5, 6} 

 { x for x in range(10)} #   set([1, 2, 3]) == {1, 2, 3} set((i*2 for i in range(10))) == {i*2 for i in range(10)} 

 >>> x = 5 >>> 1 < x < 10 True >>> 10 < x < 20 False >>> x < 10 < x*10 < 100 True >>> 10 > x <= 9 True >>> 5 == x > 4 True 

 >>> NewType = type("NewType", (object,), {"x": "hello"}) >>> n = NewType() >>> nx 'hello' 

 >>> class NewType(object): >>> x = "hello" >>> n = NewType() >>> nx "hello" 

 sum[value] = sum.get(value, 0) + 1 

 >>> d = {} >>> a, b = 4, 5 >>> d[a] = list() >>> d {4: []} >>> d[a].append(b) >>> d {4: [5]} 

 x = 1 if (y == 10) else 2 # X  1,  ,  Y  10.     - X  2 x = 3 if (y == 1) else 2 if (y == -1) else 1 #   .    elif 

 >>> first,second,*rest = (1,2,3,4,5,6,7,8) >>> first #   1 >>> second #   2 >>> rest #    [3, 4, 5, 6, 7, 8] 

 >>> first,*rest,last = (1,2,3,4,5,6,7,8) >>> first 1 >>> rest [2, 3, 4, 5, 6, 7] >>> last 8 

 >>> l = ["spam", "ham", "eggs"] >>> list(enumerate(l)) >>> [(0, "spam"), (1, "ham"), (2, "eggs")] >>> list(enumerate(l, 1)) #        >>> [(1, "spam"), (2, "ham"), (3, "eggs")] 

 try: function() except Error: #    try    Error else: #   try    except finally: #     

 >>> x = [1, 2, 3] >>> y = x >>> y[2] = 5 >>> y [1, 2, 5] >>> x [1, 2, 5] 

 >>> x = [1,2,3] >>> y = x[:] >>> y.pop() 3 >>> y [1, 2] >>> x [1, 2, 3] 

 import copy my_dict = {'a': [1, 2, 3], 'b': [4, 5, 6]} my_copy_dict = copy.deepcopy(my_dict) 

 >>> l = ['a', 'b', 'c', 'd', 'e'] >>> for i, value_list in enumerate(l, 1): #  1 -   >>> print(i, value_list) ... 1 a 2 b 3 c 4 d 5 e 

 >>> def foo(x=[]): ... x.append(1) ... print x ... >>> foo() [1] >>> foo() [1, 1] #    [1] >>> foo() [1, 1, 1] 

 >>> def foo(x=None): ... if x is None: ... x = [] ... x.append(1) ... print x >>> foo() [1] >>> foo() [1] 

 class MyDict(dict): #    def __missing__(self, key): return key ... >>> m = MyDict(a=1, b=2, c=3) #     >>> m {'a': 1, 'c': 3, 'b': 2} >>> m['a'] #     1 1 >>> m['z'] #         'z' 

 >>> def print_args(function): >>> def wrapper(*args, **kwargs): >>> print ' : ', args, kwargs >>> return function(*args, **kwargs) >>> return wrapper >>> @print_args >>> def write(text): >>> print text >>> write('foo') Arguments: ('foo',) {} foo 

 @f1(arg) @f2 def func(): pass 

 def func(): pass func = f1(arg)(f2(func)) 

 >>> a = 10 >>> b = 5 >>> a, b (10, 5) >>> a, b = b, a >>> a, b (5, 10) 

 >>> def jim(phrase): ... return 'Jim says, "%s".' % phrase >>> def say_something(person, phrase): ... print person(phrase) >>> say_something(jim, 'hey guys') #     'Jim says, "hey guys".' 

 #      g(),       . #       "100" (  (7+3)×(7+3)). def f(x): return x + 3 def g(function, x): return function(x) * function(x) print g(f, 7) 

 >>> round(1234.5678, -2) 1200.0 >>> round(1234.5678, 2) 1234.57 

 import this 

 from __future__ import braces 

 a = [1,2,3,4,5] >>> a[::2] #   [1,3,5] 

 >>> a[::-1] #   [5,4,3,2,1] 

 import webbrowser webbrowser.open_new_tab('http://habrahabr.ru/') #  True    

 a = [(1,2), (3,4), (5,6)] zip(*a) # [(1, 3, 5), (2, 4, 6)] 

 >>> t1 = (1, 2, 3) >>> t2 = (4, 5, 6) >>> dict (zip(t1,t2)) {1: 4, 2: 5, 3: 6} 

 >>> a = range(10) >>> a [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> a[:5] = [42] #    5   "42" >>> a [42, 5, 6, 7, 8, 9] >>> a[:1] = range(5) >>> a [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> del a[::2] #     >>> a [1, 3, 5, 7, 9] >>> a[::2] = a[::-2] #  reserved >>> a [9, 3, 5, 7, 1] 

 >>> m = {} >>> m.setdefault('foo', []).append(1) >>> m {'foo': [1]} >>> m.setdefault('foo', []).append(2) >>> m {'foo': [1, 2]} 

 import antigravity 

 >>> for n in range(2, 10): ... for x in range(2, n): ... if n % x == 0: ... print n, 'equals', x, '*', n/x ... break ... else: ... # loop fell through without finding a factor ... print n, 'is a prime number' 

 import __hello__ 

 >>> #    >>> d = {'banana': 3, 'apple':4, 'pear': 1, 'orange': 2} >>> #     >>> OrderedDict(sorted(d.items(), key=lambda t: t[0])) OrderedDict([('apple', 4), ('banana', 3), ('orange', 2), ('pear', 1)]) >>> #    >>> OrderedDict(sorted(d.items(), key=lambda t: t[1])) OrderedDict([('pear', 1), ('orange', 2), ('banana', 3), ('apple', 4)]) >>> #      >>> OrderedDict(sorted(d.items(), key=lambda t: len(t[0]))) OrderedDict([('pear', 1), ('apple', 4), ('orange', 2), ('banana', 3)]) 

 class Worm: def creep(self): print("i am creeping") class Butterfly: def fly(self): print("i am flying") creature = Worm() creature.creep() creature.__class__ = Butterfly creature.fly() 

 from collections import Counter Counter('habrahabr') # Counter({'a': 3, 'h': 2, 'r': 2, 'b': 2}) 

 assert x>y 

 assert <test>, <data> 

  if __debug__: if not <test>: raise AssertationError, <data>