This does not work:
print((lambda : return None)())
But this does:
print((lambda : None)())
Why?
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1Why would you want to? Do you have a specific example we can help with?John Zwinck– John Zwinck2016-05-04 09:58:41 +00:00Commented May 4, 2016 at 9:58
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1I m trying to give an educational example of the most simplistic lambda function - empty lambdaERJAN– ERJAN2016-05-04 09:59:04 +00:00Commented May 4, 2016 at 9:59
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5 Answers
Because return is a statement. Lambdas can only contain expressions.
1 Comment
ERJAN
great, also insightful into the nature of lambdas - they can only contain expressions
lambda functions automatically return an expression. They cannot contain statements. return None is a statement and therefore cannot work. None is an expression and therefore works.
Comments
Lambda can execute only expressions and return result of the executed statement, return is the statement.
Consider using or and and operators to short-circuit the result for more flexibility in the values which will be returned by your lambda. See some samples below:
# return result of function f if bool(f(x)) == True otherwise return g(x)
lambda x: f(x) or g(x)
# return result of function g if bool(f(x)) == True otherwise return f(x).
lambda x: f(x) and g(x)
Comments
because lambda takes a number of parameters and an expression combining these parameters, and creates a small function that returns the value of the expression.
Comments
Remember a lambda can call another function which can in turn return anything (Even another lambda)
# Does what you are asking... but not very useful
return_none_lambda = lambda : return_none()
def return_none():
return None
# A more useful example that can return other lambdas to create multipier functions
multiply_by = lambda x : create_multiplier_lambda(x)
def create_multiplier_lambda(x):
return lambda y : x * y
a = multiply_by(4)
b = multiply_by(29)
print(a(2)) # prints 8
print(b(2)) # prints 58
