July 2017
Intermediate to advanced
398 pages
11h 54m
Chinese
Content preview from Python数据处理
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26
｜
第
2
章
加法和减法
对于
Python
的其他数据类型，你也可以做加法，例如字符串和列表。试一试下面的
代码：
'This is ' + 'awesome.'
和
['Joker', 'Simon', 'Ellie'] + ['Lishka', 'Turtle']
试试用减法，看看会发生什么？运行下面的代码会报错，你能从中学到什么？
['Joker', 'Simon', 'Ellie', 'Lishka', 'Turtle'] - ['Turtle']
你应该会得到报错信息：
TypeError: unsupported operand type(s) for -: 'list' and
'list'
。这告诉我们，
Python
列表支持加法，却不支持减法。这是因为
Python
开发人
员对每种数据类型支持的方法所做的选择。如果你想了解如何对列表做减法，可以查看
Python
官网上列表的
remove
方法（
https://docs.python.org/2/tutorial/datastructures.html
）。
2.3.3
列表方法
：
列表能做什么
列表有几个必须知道的方法。我们从一个空列表开始，用一个方法来添加元素。
首先，像这样定义一个空列表：
dog_names = []
在解释器中输入
dog_names
，返回的是
[]
，这是
Python
显示空列表的方式。在本章前面
的内容里，这个变量中保存了好几个名字，但在上一行代码中我们
重新定义
了这个变量，
现在它是一个空列表。内置的
append
方法可以向列表中添加元素 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.