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' ....

Answer 1

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.