如何从Python中的列表中提取与某些条件匹配的值？

Question

我是Python的新用户。我想从列表中提取特定值。我的例子是提取除-1之外的值。实现这一过程的智能方法是什么？

a = [-1, 0, 2,-1, 30]
# new_a = ?? # extract values except for -1
-> new_a = [0, 2, 30]

Answer 1

>>> a = [-1, 0, 2,-1, 30]
>>> new_a=list(filter(lambda x:x!=-1, a))
>>> print(new_a)
[0, 2, 30]

或

>>> new_a=[i for i in a if i!=-1]
>>> print(new_a)
[0, 2, 30]

或在if

内for的旧学校方式

>>> new_a=[]
>>> for i in a:
...     if i!=-1:
...         new_a+=[i]
... 
>>> print(new_a)
[0, 2, 30]

Answer 2

In [74]: a = [-1, 0, 2,-1, 30]

In [75]: list(set(a)-set([-1]))
Out[75]: [0, 2, 30]