python基礎之列表推導式

例1：

>>> List=[x for x in range(10)]
>>> List
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

等價於：

>>> List=[]
>>> for x in range(10):
	List.append(x)	
>>> List
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例2：

>>> List=[x+3 for x in range(10)]
>>> List
[3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

>>> a=[1,2,3,4,5]
>>> List=[x*2 for x in a]
>>> List
[2, 4, 6, 8, 10]

例3：兩個for循環

>>> List=[x for x in range(3) for x in range(5)]
>>> List
[0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4]

等價於：

>>> List=[]
>>> for x in range(3):
	    for x in range(5):
		    List.append(x)
>>> List
[0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4]

例4：

>>> List=[(x,y) for x in range(3) for y in range(4)]
>>> List
[(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]

等價於：

>>> List=[]
>>> for x in range(3):
	for y in range(4):
		List.append((x,y))	
>>> List
[(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]

例5：for 循環後面跟if條件語句: 用if 語句判斷，當if後面的語句值爲真時，將對應的元素放入列表

>>> List=[x for x in range(3) for x in range(8) if x%2==0] 
>>> List
[0, 2, 4, 6, 0, 2, 4, 6, 0, 2, 4, 6]

例6 ：

>>> a=[[1,2],[3,4],[5,6]]
>>> [j for i in a for j in i]
[1, 2, 3, 4, 5, 6]