Regular expression to match start of filename and filename extension


Question

What is the regular expression to match strings (in this case, file names) that start with 'Run' and have a filename extension of '.py'?

The regular expression should match any of the following:

RunFoo.py
RunBar.py
Run42.py

It should not match:

myRunFoo.py
RunBar.py1
Run42.txt

The SQL equivalent of what I am looking for is ... LIKE 'Run%.py' ....

1
18
3/8/2018 11:44:56 PM

Accepted Answer

For a regular expression, you would use:

re.match(r'Run.*\.py$')

A quick explanation:

  • . means match any character.
  • * means match any repetition of the previous character (hence .* means any sequence of chars)
  • \ is an escape to escape the explicit dot
  • $ indicates "end of the string", so we don't match "Run_foo.py.txt"

However, for this task, you're probably better off using simple string methods. ie.

filename.startswith("Run") and filename.endswith(".py")

Note: if you want case insensitivity (ie. matching "run.PY" as well as "Run.py", use the re.I option to the regular expression, or convert to a specific case (eg filename.lower()) before using string methods.

40
10/8/2008 11:48:59 PM

Warning:

  • jobscry's answer ("^Run.?.py$") is incorrect (will not match "Run123.py", for example).
  • orlandu63's answer ("/^Run[\w]*?.py$/") will not match "RunFoo.Bar.py".

(I don't have enough reputation to comment, sorry.)


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