Programming Python, Second Edition

Searching Directory Trees

Engineers love to change things. As I was writing this book, I found it almost irresistible to move and rename directories, variables, and shared modules in the book examples tree, whenever I thought I’d stumbled on to a more coherent structure. That was fine early on, but as the tree became more intertwined, this became a maintenance nightmare. Things like program directory paths and module names were hardcoded all over the place -- in package import statements, program startup calls, text notes, configuration files, and more.

One way to repair these references, of course, is to edit every file in the directory by hand, searching each for information that has changed. That’s so tedious as to be utterly impossible in this book’s examples tree, though; as I wrote these words, the example tree contained 118 directories and 1342 files! (To count for yourself, run a command-line python PyTools/visitor.py 1 in the PP2E examples root directory.) Clearly, I needed a way to automate updates after changes.

Greps and Globs in Shells and Python

There is a standard way to search files for strings on Unix and Linux systems: the command-line program grep and its relatives list all lines in one or more files containing a string or string pattern.^[43] Given that Unix shells expand (i.e., “glob”) filename patterns automatically, a command such as grep popen *.py will search a single directory’s Python files for string “popen”. Here’s such a command in action on Windows (I ...