why use lambdas functions?

Question

Wouldn't this be more simple:

x = -4
print(x**2 + 5*x + 4)

instead of this:

print((lambda x: x**2 + 5*x + 4) (-4))

Answer 1

Lambdas are useful when you want to pass some action to execute to another function. Typical cases are filter() and map(), they apply some action to the elements of a list, in order to realise a transformation of that list. They abstract the transformation and this way they can be used for any particular transformation. Lambdas here are a very practical way to define a particular action in the same line you invoke the outer function, without having to define a whole new function for it. This is a significant case for lambdas, because usually actions for filters and mappings are trivial bits of code and writing them inline is very useful.

Answer 2

lambda function are used when there is an single line expression to return from a function,and with map and filter it is precise way of writing functions and extracting values out of iterables.