How to solve lambda() takes 1 positional argument but 2 were given-CodePudding

I have the following code snippet but it is giving me the type error above. What I basically wanted to do is add two to every element and reduct it to a single sum, but it didnt work. How can we achieve this??

import functools
list1 = [1,2,3,4]
result = functools.reduce(lambda x:x 2, list1)
print(result)

Update:

It works when I do the following though:

list1 = [1,2,3,4]
result = functools.reduce(lambda x,y:x y, list1)
print(result)

CodePudding user response：

reduce() requires a lambda function which takes 2 arguments. The first argument is the collector. But here, so that 2 is applied also on the first argument, you have to give the initial value 0.

import functools
list1 = [1,2,3,4]
result = functools.reduce(lambda acc, el: acc   el   2, list1, 0)
print(result) ## sum([3, 4, 5, 6]) = 18

You basically want to do a normal summing reduce(lambda x, y: x y, lst) => sum(lst) and a map(lambda x: x 2, l) which is expressed in a more pythonic way as a list comprehension:

l = [1, 2, 3, 4]
sum([x   2 for x in l])            # most pythonic!
## 18
sum(map(lambda x: x   2, l))
## 18

or:

import functools
l = [1, 2, 3 ,4]
result = functools.reduce(lambda x, y: x   y, [x   2 for x in l])
result ## 18

or:

import functools
l = [1, 2, 3 ,4]
result = functools.reduce(lambda x, y: x   y, map(lambda x: x   2, l))
result ## 18

CodePudding user response：

The callable passed to the reduce function needs to take two arguments to aggregate the current result with the next item from the given iterable:

import functools

list1 = [1, 2, 3, 4]
result = functools.reduce(lambda x, y: x   y   2, list1, 0)
print(result)

This outputs: