What's this?

I'm curious about when to use the Lambda function, so I'll investigate the topic.

What I learned

In Python, you usually use def to create functions.

But, the lambda function can create a small and anonymous function.

It's basically a syntactic sugar for a normal function.

You can create a one-liner function using the lambda function.

sum_a_b = lambda a, b: a + b
print(sum_a_b(1, 3)) # => 4

It is syntactically restricted to a single expression, but you can use an if statement to switch which to return.

return_bigger = lambda a,b: a if a > b else b
print(return_bigger(1, 3)) # => 3

The above cases are not realistic use cases, because if you'd like to create a named function, you can use normal functions using def.

When you'd like to use functions as arguments, lambda functions are useful.

For example, let's check a case using map.
The map function returns an iterator that applies function to every item of an iterable.

Of course, you can create a function and use it in the map function.

l = [1, 2, 3, 4]

def double(x):
    return x**2

print(list(map(double, l))) # => [1, 4, 9, 16]

Also, you can use the lambda function, and it makes the code simpler.

l = [1, 2, 3, 4]
print(list(map(lambda x: x**2, l))) # => [1, 4, 9, 16]

Abbreviated notations like this may sometimes decrease readability. You should use it properly.