SyntaxError: invalid syntax when using Match case in Python

# SyntaxError: invalid syntax when using Match case in Python

The "SyntaxError: invalid syntax when using Match case" error is most often caused when:

1. Using a Python version that is older than 3.10.
2. Having a syntactical error before the Match-Case statement.
3. Having a syntactical error in the Match-Case statement.

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  File "/home/borislav/Desktop/bobbyhadz_python/main.py", line 2
    match status:
          ^
SyntaxError: invalid syntax

The syntax for Structural Pattern Matching is the following.

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match subject:
    case <pattern_1>:
        <action_1>
    case <pattern_2>:
        <action_2>
    case <pattern_3>:
        <action_3>
    case _:
        <action_wildcard>

Here is an example that prints a string that corresponds to the provided status code.

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def http_error(status):
    match status:
        case 200:
            return "OK"
        case 400:
            return "Bad request."
        case 404:
            return "Page not found"
        case 500:
            return "Internal Server error"
        case _:
            return "Something went wrong"


print(http_error(400)) # 👉️ Bad request

However, if I run the exact same code sample using a Python version older than 3.10, I'd get the error.

Notice that I ran the code with Python 3.9, which caused the SyntaxError because Structural Pattern Matching has been added in Python 3.10.

# Checking your version of Python

You can use the python --version command to check your version of Python.

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python --version

python3 --version

Alternatively, you can access the version attribute on the sys module.

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import sys

print(sys.version)

Run your code with python module_name.py to get your Python version.

If you have an older Python version than 3.10, download the latest version from the official python.org website.

# Implementing your own Match-case statement

If you aren't able to switch to a version of Python that is greater than or equal to Python 3.10, you can implement your own Match-Case statement.

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def http_error(status):

    status_dict = {
        200: 'OK',
        400: 'Bad request',
        404: 'Not Found',
        500: 'Internal Server error',
    }

    default_status = 'Something went wrong'

    return status_dict.get(status, default_status)


print(http_error(200))  # 👉️ OK
print(http_error(400))  # 👉️ Bad request
print(http_error(10000))  # 👉️ Something went wrong

If the supplied status is not one of the possible values, we return a default value.

The dict.get() method returns the value for the given key if the key is in the dictionary, otherwise a default value is returned.

The method takes the following 2 parameters:

If a value for the default parameter is not provided, it defaults to None, so the get() method never raises a KeyError.

# Having a syntactical error right before the Match-Case statement

Another common cause of the error is having a syntactical error right before the Match-Case statement.

Make sure all the parentheses, curly braces, square brackets, single and double quotes match and have been closed.

You can comment out the Match-Case statement and run your code to verify if it is the cause of the error.

The syntax for Structural Pattern Matching is the following.

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match subject:
    case <pattern_1>:
        <action_1>
    case <pattern_2>:
        <action_2>
    case <pattern_3>:
        <action_3>
    case _:
        <action_wildcard>

The match statement takes a value and compares it to the patterns in the case blocks.

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def http_error(status):
    match status:
        case 200:
            return "OK"
        case 400:
            return "Bad request."
        case 404:
            return "Page not found"
        case 500:
            return "Internal Server error"
        case _:
            return "Something went wrong"


print(http_error(200))  # 👉️ OK
print(http_error(400))  # 👉️ Bad request
print(http_error(10000))  # 👉️ Something went wrong

# Conclusion

To solve the "SyntaxError: invalid syntax when using Match case" error, make sure:

1. You're using a Python version that is greater than or equal to 3.10.
2. You don't have any syntactical errors before the Match-Case statement.
3. You don't have any syntactical errors in the Match-Case statement.