How Can I Return a Predefined List in Python Based on String Input?

Returning a Pre-determined Value Based on String Input

In Python, we sometimes encounter the need to return a specific list based on a provided string. This can be achieved using various methods, one of which involves leveraging dictionaries.

Using a Dictionary

The most straightforward approach is to define a dictionary where keys represent the string inputs and corresponding values are the desired lists.

get_ext = {'text': ['txt', 'doc'],
            'audio': ['mp3', 'wav'],
            'video': ['mp4', 'mkv']
}

To retrieve the desired list, simply access the appropriate key:

get_ext['video']
# Output: ['mp4', 'mkv']

Using a Function with the Dictionary

If prefer a function-based solution, you can assign the get method of the dictionary to a variable:

get_ext = get_ext.get

This function will return the list for the specified key or None if the key doesn't exist.

get_ext('video')
# Output: ['mp4', 'mkv']

Using a Custom Default Value

To specify a custom default value for unknown keys, consider using a wrapper function:

def get_ext(file_type):
    types = {'text': ['txt', 'doc'],
             'audio': ['mp3', 'wav'],
             'video': ['mp4', 'mkv']
    }

    return types.get(file_type, [])

This function will return an empty list for unknown keys.

Addressing Performance Concerns

For performance-conscious applications, it's worth noting that the types dictionary in the wrapper function is recreated every time the function is called. To optimize this, you can create a class and initialize the types dictionary within the constructor, ensuring it's only created once.

class get_ext(object):
    def __init__(self):
        self.types = {'text': ['txt', 'doc'],
                      'audio': ['mp3', 'wav'],
                      'video': ['mp4', 'mkv']
        }

    def __call__(self, file_type):
        return self.types.get(file_type, [])

get_ext = get_ext()

This class-based approach enables easy modification of the recognized file types while maintaining performance efficiency.

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