Pattern Matching with glob

diagram the three things glob quietly does not do mermaid

  flowchart TD
  A["glob('*.txt')"] --> B["the current directory only"]
  C["glob('**/*.txt')"] --> D["still one level -- ** acts like * without recursive=True"]
  E["glob('**/*.txt', recursive=True)"] --> F["every depth, including the top"]
  G["a dotfile like .hidden.txt"] --> H["never matched by * -- needs '.*' explicitly"]
  I["b.TXT vs pattern *.txt"] --> J["matched here on Windows; would NOT on Linux"]
  F --> K["for recursion, Path('.').rglob('*.txt') is clearer"]
  H --> L["and rglob DOES return dotfiles -- the two differ"]

A pattern that looks like it should match everything usually does not. Two stars only recurse if you ask for recursion, a leading dot has to be matched explicitly, and case sensitivity depends on the filesystem rather than on your pattern. All three were measured on the same small tree.

Measured on one tree: glob and rglob do not agree

Files present: a.txt, b.TXT, .hidden.txt, sub/c.txt, sub/deep/d.txt, sub/e.md.

Call	Returns
glob("*.txt")	a.txt, b.TXT
glob("**/*.txt")	sub/c.txt — one level, ** behaved like *
glob("**/*.txt", recursive=True)	a.txt, b.TXT, sub/c.txt, sub/deep/d.txt
Path(".").rglob("*.txt")	the same plus .hidden.txt

Three separate traps in one table.

** does nothing without recursive=True. The pattern is accepted either way, so the script runs and silently processes a fraction of the files.

Dotfiles are invisible to glob — .hidden.txt is absent from *.txt and needs a pattern starting with a literal dot. pathlib.rglob does not share that behaviour and returns it.

Case sensitivity is the filesystem’s, not the pattern’s. b.TXT matched *.txt here on Windows and would not on Linux — so a script tested on one and deployed on the other silently processes a different set of files.

What glob does

glob finds files using wildcard patterns:

• *.txt
• data_??.csv
• recursive patterns with **

Using glob module

glob_basic.py

from glob import glob
 
for path in glob("*.py"):
    print(path)

Recursive glob

glob_recursive.py

from glob import glob
 
for path in glob("**/*.md", recursive=True):
    print(path)

Prefer pathlib

pathlib.Path.rglob is often cleaner.

🧪 Try It Yourself

Exercise 1 – List Files with os.listdir

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Exercise 2 – Join Paths with os.path.join

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Exercise 3 – Write and Read a File

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