In [1]: def append_to_list(value, def_list=[]):
   ...:         def_list.append(value)
   ...:         return def_list
   ...:

In [2]: my_list = append_to_list(1)

In [3]: my_list
Out[3]: [1]

In [4]: my_other_list = append_to_list(2)

In [5]: my_other_list
Out[5]: [1, 2] # 看到了吧，其實我們本來只想生成[2] 但是卻把第一次運行的效果頁帶了進來

In [6]: import time

In [7]: def report_arg(my_default=time.time()):
   ...:         print(my_default)
   ...:

In [8]: report_arg() # 第一次執(zhí)行
1399562371.32

In [9]: time.sleep(2) # 隔了2秒

In [10]: report_arg()
1399562371.32 # 時間竟然沒有變

def append_to_list(element, to=None):
    if to is None:
        to = []
    to.append(element)
    return to

In [12]: gen = (i for i in range(5))

In [13]: 2 in gen
Out[13]: True

In [14]: 3 in gen
Out[14]: True

In [15]: 1 in gen
Out[15]: False # 1為什么不在gen里面了? 因為調(diào)用1->2,這個時候1已經(jīng)不在迭代器里面了,被按需生成過了

In [20]: gen = (i for i in range(5))

In [21]: a_list = list(gen) # 可以轉(zhuǎn)化成列表，當(dāng)然a_tuple = tuple(gen) 也可以

In [22]: 2 in a_list
Out[22]: True

In [23]: 3 in a_list
Out[23]: True

In [24]: 1 in a_list # 就算循環(huán)過,值還在
Out[24]: True

In [29]: my_list = [lambda: i for i in range(5)]

In [30]: for l in my_list:
   ....:         print(l())
   ....:
4
4
4
4
4

In [31]: my_gen = (lambda: n for n in range(5))

In [32]: for l in my_gen:
   ....:         print(l())
   ....:
0
1
2
3
4

In [33]: my_list = [lambda x=i: x for i in range(5)] # 看我給每個lambda表達式賦了默認(rèn)值

In [34]: for l in my_list:
   ....:         print(l())
   ....:
0
1
2
3
4

In [35]: def groupby(items, size):
   ....:     return zip(*[iter(items)]*size)
   ....:

In [36]: groupby(range(9), 3)
Out[36]: [(0, 1, 2), (3, 4, 5), (6, 7, 8)]

In [39]: [iter(items)]*3
Out[39]:
[<listiterator at 0x10e155fd0>,
 <listiterator at 0x10e155fd0>,
 <listiterator at 0x10e155fd0>] # 看到了吧, 其實就是把items變成可迭代的, 重復(fù)三回（同一個對象哦）, 但是別忘了,每次都.next(), 所以起到了分組的作用
 In [40]: [lambda x=i: x for i in range(5)]
Out[40]:
[<function __main__.<lambda>>,
 <function __main__.<lambda>>,
 <function __main__.<lambda>>,
 <function __main__.<lambda>>,
 <function __main__.<lambda>>] # 看懂了嗎?

In [44]: a = [1, 2, 3, 4, 5]

In [45]: for i in a:
   ....:     if not i % 2:
   ....:         a.remove(i)
   ....:

In [46]: a
Out[46]: [1, 3, 5] # 沒有問題

In [50]: b = [2, 4, 5, 6]

In [51]: for i in b:
   ....:      if not i % 2:
   ....:          b.remove(i)
   ....:

In [52]: b
Out[52]: [4, 5] # 本來我想要的結(jié)果應(yīng)該是去除偶數(shù)的列表