13.9 通過(guò)文件名查找文件

問(wèn)題

You need to write a script that involves finding files, like a file renaming script or a logarchiver utility, but you’d rather not have to call shell utilities from within your Pythonscript, or you want to provide specialized behavior not easily available by “shelling out.”

解決方案

To search for files, use the os.walk() function, supplying it with the top-level directory.Here is an example of a function that finds a specific filename and prints out the fullpath of all matches:

!/usr/bin/env python3.3import os

def findfile(start, name):for relpath, dirs, files in os.walk(start):if name in files:full_path = os.path.join(start, relpath, name)print(os.path.normpath(os.path.abspath(full_path)))if name == ‘main':findfile(sys.argv[1], sys.argv[2])
Save this script as findfile.py and run it from the command line, feeding in the startingpoint and the name as positional arguments, like this:

bash % ./findfile.py . myfile.txt

討論

The os.walk() method traverses the directory hierarchy for us, and for each directoryit enters, it returns a 3-tuple, containing the relative path to the directory it’s inspecting,a list containing all of the directory names in that directory, and a list of filenames inthat directory.For each tuple, you simply check if the target filename is in the files list. If it is,os.path.join() is used to put together a path. To avoid the possibility of weird lookingpaths like ././foo//bar, two additional functions are used to fix the result. The first isos.path.abspath(), which takes a path that might be relative and forms the absolutepath, and the second is os.path.normpath(), which will normalize the path, therebyresolving issues with double slashes, multiple references to the current directory, andso on.Although this script is pretty simple compared to the features of the find utility foundon UNIX platforms, it has the benefit of being cross-platform. Furthermore, a lot ofadditional functionality can be added in a portable manner without much more work.To illustrate, here is a function that prints out all of the files that have a recent modifi‐cation time:

!/usr/bin/env python3.3

import osimport time

def modified_within(top, seconds):
now = time.time()for path, dirs, files in os.walk(top):

for name in files:> fullpath = os.path.join(path, name)if os.path.exists(fullpath):

mtime = os.path.getmtime(fullpath)if mtime > (now - seconds):

print(fullpath)

if name == ‘main':
import sysif len(sys.argv) != 3:

print(‘Usage: {} dir seconds'.format(sys.argv[0]))raise SystemExit(1)

modified_within(sys.argv[1], float(sys.argv[2]))

It wouldn’t take long for you to build far more complex operations on top of this littlefunction using various features of the os, os.path, glob, and similar modules. See Rec‐ipes 5.11 and 5.13 for related recipes.