August 2017
Intermediate to advanced
274 pages
7h 44m
Chinese
Content preview from Python数据分析基础
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58
｜
第
2
章
假设输入文件和
Python
脚本都保存在你的桌面上，你也没有在命令行或终端行窗口中改变
目录，在命令行中输入以下命令，然后按回车键运行脚本（如果你使用
Mac
，需要对新的
脚本先运行
chmod
命令，使它成为可执行的）：
python 2csv_reader_parsing_and_write.py supplier_data.csv\
output_files\2output.csv
你可以看到输出被打印到屏幕上，如图
2-9
所示。
图 2-9：运行 Python 脚本得到的输出
输入文件中的所有行都被打印到了屏幕上，同时被写入到输出文件。你可以看到，
Python
内置的
csv
模块处理了嵌入数据的逗号问题，正确地将每一行拆分成了
5
个值。
我们知道了如何使用
csv
模块来读取、处理和写入
CSV
文件，下面开始学习如何筛选出特
定的行以及如何选择特定的列，以便可以有效地抽取出需要的数据。
2.2
筛选特定的行
有些时候，你并不需要文件中所有的数据。例如，你可能只需要一个包含特定词或数字的
行的子集，或者是与某个具体日期关联的行的子集。在这些情况下，可以用
Python
筛选出
特定的行来使用。
你应该很熟悉如何在
Excel
中手动筛选行，但是本章的重点在于提高你的能力，使你既能
处理因为体积太大以致
Excel
不能打开的
CSV
文件，又能处理多个
CSV
文件。因为要通
过手动处理这些文件，时间花费太多了。
下面各小节演示了在输入文件中筛选出特定行的
3
种方法：
•
行中的值满足某个条件
•
行中的值属于某个集合
•
行中的值匹配于某个模式（正则表达式） ...
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