Failure when filtering string list with re.match [duplicate]

Question

I'd like to filter a list of strings in python by using regex. In the following case, keeping only the files with a '.npy' extension.

The code that doesn't work:

import re  files = [ '/a/b/c/la_seg_x005_y003.png',           '/a/b/c/la_seg_x005_y003.npy',           '/a/b/c/la_seg_x004_y003.png',           '/a/b/c/la_seg_x004_y003.npy',           '/a/b/c/la_seg_x003_y003.png',           '/a/b/c/la_seg_x003_y003.npy', ]  regex = re.compile(r'_x\d+_y\d+\.npy')  selected_files = filter(regex.match, files) print(selected_files) 

The same regex works for me in Ruby:

selected = files.select { |f| f =~ /_x\d+_y\d+\.npy/ } 

What's wrong with the Python code?

Answer 1

selected_files = filter(regex.match, files) 

re.match('regex') equals to re.search('^regex') or text.startswith('regex') but regex version. It only checks if the string starts with the regex.

So, use re.search() instead:

import re  files = [ '/a/b/c/la_seg_x005_y003.png',           '/a/b/c/la_seg_x005_y003.npy',           '/a/b/c/la_seg_x004_y003.png',           '/a/b/c/la_seg_x004_y003.npy',           '/a/b/c/la_seg_x003_y003.png',           '/a/b/c/la_seg_x003_y003.npy', ]  regex = re.compile(r'_x\d+_y\d+\.npy')  selected_files = list(filter(regex.search, files)) # The list call is only required in Python 3, since filter was changed to return a generator print(selected_files) 

Output:

['/a/b/c/la_seg_x005_y003.npy',  '/a/b/c/la_seg_x004_y003.npy',  '/a/b/c/la_seg_x003_y003.npy'] 

---

And if you just want to get all of the .npy files, str.endswith() would be a better choice:

files = [ '/a/b/c/la_seg_x005_y003.png',           '/a/b/c/la_seg_x005_y003.npy',           '/a/b/c/la_seg_x004_y003.png',           '/a/b/c/la_seg_x004_y003.npy',           '/a/b/c/la_seg_x003_y003.png',           '/a/b/c/la_seg_x003_y003.npy', ]   selected_files = list(filter(lambda x: x.endswith('.npy'), files))  print(selected_files)