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Regular expression to match start of filename and filename extension

Answer #1 98.2 %

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.

Answer #2 100 %

I don't really understand why you're after a regular expression to solve this 'problem'. You're just after a way to find all .py files that start with 'Run'. So this is a simple solution that will work, without resorting to compiling an running a regular expression:

import os
for filename in os.listdir(dirname):
    root, ext = os.path.splitext(filename)
    if root.startswith('Run') and ext == '.py':
        print filename
Answer #3 100 %

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.)

Answer #4 100 %
/^Run.*\.py$/

Or, in python specifically:

import re
re.match(r"^Run.*\.py$", stringtocheck)

This will match "Runfoobar.py", but not "runfoobar.PY". To make it case insensitive, instead use:

re.match(r"^Run.*\.py$", stringtocheck, re.I)
Answer #5 100 %

You don't need a regular expression, you can use glob, which takes wildcards e.g. Run*.py

For example, to get those files in your current directory...

import os, glob
files = glob.glob( "".join([ os.getcwd(), "\\Run*.py"]) )

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