One of the most important uses of Python for data processing is the reading, changing, and writing of text files. Data is often stored in text files, because text files can be easily transferred between different programs. There are multiple standardized formats for text files, such as “comma-separated values” (CSV) files. Python supports particular text file formats through modules, some of which will be discussed later. This chapter focusses on opening, reading, writing, and closing of any text file, regardless of format.