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pythonlambda

Python's lambda with underscore for an argument?

What does the following code do?

a = lambda _:True

From what I read and tested in the interactive prompt, it seems to be a function that returns always True.

Am I understanding this correctly? I hope to understand why an underscore (_) was used as well.

Solution

  • The _ is variable name. Try it. (This variable name is usually a name for an ignored variable. A placeholder so to speak.)

    Python:

    >>> l = lambda _: True
>>> l()
<lambda>() missing 1 required positional argument: '_'

>>> l("foo")
True

    So this lambda does require one argument. If you want a lambda with no argument that always returns True, do this:

    >>> m = lambda: True
>>> m()
True