list comprehensions allow you to create lists with a for loop with less code.
可以在 list 中使用 for 迴圈的一種方式
>>> comp_list = [x * 2 for x in range(10)]
>>> print(comp_list)
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
>>> comp_list_2 = [x ** 2 for x in range(7) if x % 2 == 0]
>>> print(comp_list_2)
[4, 16, 36]Iterable is a “sequence” of data, you can iterate over using a loop.
Iterable 指的是 a “sequence” of data，也就是可以透過 loop 來遍尋。例如 list 就是一個 Iterable 物件，其他還有 strings, dicts, tuples, sets
這些物件中都含有 iter() method ，可以透過 hasattr() 來檢查
>>> hasattr(str, '__iter__')
True
>>> hasattr(bool, '__iter__')
False- iter a dicts
In Python, generators provide a convenient way to implement the iterator protocol. Generator is an iterable created using a function with a yield statement.
Generator 就是利用 yield 把 function 變成 iterable，回傳值是一個 generator object
yield 跟 return 很像，只是 return 的時候 function call stack 會被清掉，下一次再 call 會重新來。yield 則是下次呼叫時，可以從上次還未執行到的部分繼續執行，而不是重新建立一個新 stack。
可以使用 next & send
- next
def yield_function():
i = 0
yield i
i = 1
yield i
generator = yield_function()
print generator.next()
print ('restart')
print generator.next()會印出
0
restart
1或是使用變數去接 yield
def yield_function():
i = 0
a = yield i
i = 1
yield a
generator = yield_function()
print generator.next()
print ('restart')
print generator.next()會印出
0
restart
none- send
可以從呼叫 function 的地方得到參數帶入 yield
def yield_function():
i = 0
a = yield i
i = 1
yield a
generator = yield_function()
print generator.next()
print ('restart')
print generator.send(8)會印出
0
restart
8- generator function output
generator function 會回傳 generator object，需要用 list 轉換
def scramble(seq):
for i in range(len(seq)):
yield seq[i:] + seq[:i]
>>> scramble('spam')
<generator object scramble at 0x10a017db0>
>>> list(scramble('spam'))
['spam', 'pams', 'amsp', 'mspa']https://segmentfault.com/a/1190000000640834
- http://www.runoob.com/python3/python3-tutorial.html
- https://openhome.cc/Gossip/CodeData/PythonTutorial/index.html
- https://github.com/qiwsir/ITArticles/blob/master/BasicPython/index.md
https://medium.freecodecamp.org/python-list-comprehensions-vs-generator-expressions-cef70ccb49db