在Python3中的过滤器 [英] Filters in Python3

问题描述

我正在学习Python中过滤器的概念。

 >>> def f（x）：return x％2！= 0 and x％3！= 0 
>>> filter（f，range（2，25））
  

但是，这样的消息。

 < 0x00FDC550的过滤器对象> 
  

这是什么意思？这是否意味着我的过滤对象列表出来是存储在该内存位置？如何获得我需要的列表？

解决方案

看起来您正在使用python 3.x.在python3中， filter ， map ， zip ，等等一个可迭代的对象，但不是一个列表。换句话说，

  filter（func，data）#python 2.x 
  
 
 
相当于：
 
 $ $ p $  list（filter func，data））#python 3.x 
  

我认为这是因为你以懒惰的方式进行过滤 - 只要迭代器返回列表在迭代过程中的相同内容，就不需要耗尽所有内存来预先创建列表。

如果您熟悉列表解析和生成器表达式，那么上面的过滤器现在（几乎）等同于python3.x中的以下内容：

 （x for data in func（x））
  

相对于：

  [x for data in func（x）] 
  

in python 2.x

I am learning the concept of filters in Python. I am running a simple code like this.

>>> def f(x): return x % 2 != 0 and x % 3 != 0
>>> filter(f, range(2, 25))

But instead of getting a list, I am getting some message like this.

<filter object at 0x00FDC550>

What does this mean? Does it means that my filtered object i.e list to come out is stored at that memory location? How do I get the list which I need?

解决方案

It looks like you're using python 3.x. In python3, filter, map, zip, etc return an object which is iterable, but not a list. In other words,

filter(func,data) #python 2.x

is equivalent to:

list(filter(func,data)) #python 3.x

I think it was changed because you (often) want to do the filtering in a lazy sense -- You don't need to consume all of the memory to create a list up front, as long as the iterator returns the same thing a list would during iteration.

If you're familiar with list comprehensions and generator expressions, the above filter is now (almost) equivalent to the following in python3.x:

( x for x in data if func(x) ) 

As opposed to:

[ x for x in data if func(x) ]

in python 2.x

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