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I sometimes find myself wanting to make placeholder 'do nothing' lambda expressions, similar to saying:
def do_nothing(*args): pass But the following syntax is illegal since lambda expressions attempt to return whatever is after the colon, and you can't return pass.
do_nothing = lambda *args: pass So I was wondering, would the following expression be a suitable replacement for the above?
do_nothing = lambda *args: None Since the do_nothing function above technically returns None, is it okay to make a lambda expression that returns None to use as a placeholder lambda expression? Or is it bad practice?
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Calling type(None) will return you the NoneType constructor, which you can use for doing nothing: type(None)() . Keep in mind that the NoneType constructor only takes 0 arguments. In Python 2, though, creating instances of NoneType is impossible, so lambda: None would make the most sense.
A Python lambda function behaves like a normal function in regard to arguments. Therefore, a lambda parameter can be initialized with a default value: the parameter n takes the outer n as a default value. The Python lambda function could have been written as lambda x=n: print(x) and have the same result.
What are lambda functions in Python? In Python, an anonymous function is a function that is defined without a name. While normal functions are defined using the def keyword in Python, anonymous functions are defined using the lambda keyword. Hence, anonymous functions are also called lambda functions.
This:
def do_nothing(*args): pass is equivalent to:
lambda *args: None With some minor differences in that one is a lambda and one isn't. (For example, __name__ will be do_nothing on the function, and <lambda> on the lambda.) Don't forget about **kwargs, if it matters to you. Functions in Python without an explicit return <x> return None. This is here:
A call always returns some value, possibly None, unless it raises an exception.
I've used similar functions as default values, say for example:
def long_running_code(progress_function=lambda percent_complete: None): # Report progress via progress_function. If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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