python - 使用 re.match 过滤字符串列表时失败

Question

这个问题在这里已经有了答案:

What is the difference between re.search and re.match? (9 个回答)

关闭 3年前。

我想使用正则表达式过滤 python 中的字符串列表。在以下情况下，仅保留扩展名为“.npy”的文件。

不起作用的代码:

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)

同样的正则表达式在 Ruby 中也适用于我:

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

Python 代码有什么问题？

Answer 1

selected_files = filter(regex.match, files)

re.match('regex')等于 re.search('^regex') 或 text.startswith('regex') 但正则表达式版本。 它只检查字符串是否以正则表达式开头。

所以，请改用 re.search():

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)

输出:

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

---

如果您只想获取所有 .npy 文件，str.endswith()会是更好的选择:

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)