What Does the Underscore Variable (_) Mean in Python?

Understanding the Purpose of the Single Underscore Variable in Python (_)

Python programmers often encounter the single underscore variable (_), leaving them wondering about its significance. This article delves into its three primary conventional uses:

1. Last Executed Expression Container: In interactive interpreter sessions, _ holds the result of the most recent expression, mirroring the CPython interpreter's behavior.
2. Translation Lookup: In internationalization (i18n), _ assists in translation, allowing code like "raise forms.ValidationError(_("Please enter a correct username"))".

3. "Throwaway" Variable: _ finds use as a disposable variable for several purposes:

   • Disregarding Function Result Parts: Code like "label, has_label, = text.partition(':')", where discards the parsed result.
   • Unused Function Parameters: In function signatures, _ can indicate unnecessary parameters, such as "def callback(_):n return True".

It's important to note that using as a "throwaway" variable can conflict with its use in translation lookup. To avoid confusion, consider using _ as the disposable variable.

Linters often flag unused variables denoted by _, prompting programmers to either use them or eliminate them to avoid potential bugs or typos.

In Python 3.10, pattern matching further solidified the role of _ as a "wildcard" pattern, allowing it to cover any value without binding to a specific variable.

While _ remains a valid variable name, keep in mind that it can still maintain references to objects, affecting memory usage. For graceful resource cleanup, explicitly calling "del _" will both satisfy linters and release referenced objects.

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