Does python match does not work with list?

extension is a list of the form ["filename", "extension"], it will never match a single-element list.

You need to match only on the second element:

case [_, "jpg"]:
    print("this is a jpg file")
case [_, "gif"]:
    print("this is a gif file")

However, if the filename includes multiple . then this will break because extension will have an unknown number of elements. This can be resolved in several ways:

• Using *_ instead of _

• Using os.path.splitext(filename)[-1] to get the extension (with the .) in the safest manner:

  import os
  
  extension = os.path.splitext(filename)[-1]
  
  match extension:
      case ".jpg":
          print("this is a jpg file")
      case ".gif":
          print("this is a gif file")
      case _:
          print("error") 
  

When you split your string, it creates a list to contain all the fragments.

extension = filename.split(".")

>>> print(type(extension), extension)
<class 'list'> ['hello', 'jpg']

You should select the specific string you are interested in. In this case, it would be the last element in the list, presumably. To achieve this, you could use:

extension[-1]

>>> print(type(extension[-1]), extension[-1])
<class 'str'> jpg

Issue: You are using split() which returns a list (e.g. ['data', 'gif']). You are comparing this with a list that contains just the file extension (e.g. ['gif']). This will result in False.

Assumption: The filename is valid and has an extension e.g. image.gif.

Solution 1 - Using index: In this case, the last element in the list is the extension so you can use this for matching. An index of -1 will return the last element in the list.

filename = input('Enter filename: ')
extension = filename.split('.')

match extension[-1]:
    case 'jpg':
        print('this is a jpg file')
    case 'gif':
        print('this is a gif file')
    case _:
        print('error')

Solution 2 - Using list: Alternatively, if you wish to use the result of split() directly then you can do so as follows:

filename = input('Enter filename: ')
extension = filename.split(".")

match extension:
    case [*_, 'jpg']:
        print('this is a jpg file')
    case [*_, 'gif']:
        print('this is a gif file')
    case _:
        print('error')

Note, we use *_ as there could be file names with multiple . thus resulting in a list with more than two items.

Match on Pathlib.suffix :

from pathlib import Path

filename = input("Enter filename: ")
extension = Path(filename).suffix

match extension:
    case ".jpg":
        print("this is a jpg file")
    case ".gif":
        print("this is a gif file")
    case _:
        print("error")

Yet another option is to use os.path.splitext on the file name - although it includes the dot:

import os

path = input("Enter path: ")
match os.path.splitext()[-1]:
    case ".jpg":
        print("jpg")
    case ".png":
        print("png")

If you want to also match double extensions like in data.tar.gz, you need to use str.split combined with str.join - additionally, this code also checks for filenames with a single leading dot (so not having an extension):

path = input("Enter path: ")

split = path.split(".")
if len(split) == 1 or os.path.split(path)[-1].startswith("."):
    ext = ""
elif len(split) == 2:
    ext = split[1]
else:
    ext = split[-2] + "." + split[-1]

match ext:
    case ".jpg":
        print("jpg")
    case ".png":
        print("png")