python中for...if...構建List

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1.簡單的for...[if]...語句

>>> a=[12, 3, 4, 6, 7, 13, 21]>>> newList = [x for x in a]>>> newList[12, 3, 4, 6, 7, 13, 21]>>> newList2 = [x for x in a if x%2==0]>>> newList2[12, 4, 6]

newList構建了一個與a具有相同元素的List。但是，newList和a是不同的List。執行b=a，b和newList是不同的。

newList2是從a中選取滿足x%2==0的元素組成的List。

 

2.嵌套的for...[if]...語句

嵌套的for...[if]...語句可以從多個List中選擇滿足if條件的元素組成新的List。下面也舉幾個例子。

>>>a=[12, 3, 4, 6, 7, 13, 21]>>>b=[‘a‘, ‘b‘, ‘x‘]>>>newList=[(x, y) for x in a for y in b]>>>newList[(12, ‘a‘), (12, ‘b‘), (12, ‘x‘), (3, ‘a‘), (3, ‘b‘), (3, ‘x‘), (4, ‘a‘), (4, ‘b‘), (4, ‘x‘), (6, ‘a‘), (6, ‘b‘), (6, ‘x‘), (7, ‘a‘), (7, ‘b‘), (7, ‘x‘), (13, ‘a‘), (13, ‘b‘), (13, ‘x‘), (21, ‘a‘), (21, ‘b‘), (21, ‘x‘)]>>>newList2=[(x, y) for x in a for y in b if x%2==0 and y<‘x‘]>>>newList2[(12, ‘a‘), (12, ‘b‘), (4, ‘a‘), (4, ‘b‘), (6, ‘a‘), (6, ‘b‘)]

　　

python中for...if...構建List