# [python] How to emulate sum() using a list comprehension?

```
>>> from operator import mul
>>> nums = [1, 2, 3]
>>> reduce(mul, nums)
6
```

_{On Python 3 you will need to add this import: from functools import reduce}

In Python `2.5`

/ `2.6`

You could use `vars()['_[1]']`

to refer to the list comprehension currently under construction. This is **horrible** and should **never** be used but it's the closest thing to what you mentioned in the question (*using a list comp to emulate a product*).

```
>>> nums = [1, 2, 3]
>>> [n * (vars()['_[1]'] or [1])[-1] for n in nums][-1]
6
```

Is it possible to emulate something like sum() using list comprehension ?

For example - I need to calculate the product of all elements in a list :

```
list = [1, 2, 3]
product = [magic_here for i in list]
#product is expected to be 6
```

Code that is doing the same :

```
def product_of(input):
result = 1
for i in input:
result *= i
return result
```

It is possible to achieve by using lambda with list comprehension Since we can't assign a value in list comprehension we go with lambda

Solution:

```
>>> (lambda number_list, sum=0:[sum for number in number_list for sum in [sum + number]][-1])([1, 2, 3, 4, 5])
>>> 15
```

Something like this:

```
>>> a = [1,2,3]
>>> reduce(lambda x, y: x*y, a)
6
```

I complement the answer of Ignacio Vazquez-Abrams with some code that uses the `reduce`

operator of Python.

```
list_of_numbers = [1, 5, 10, 100]
reduce(lambda x, y: x + y, list_of_numbers)
```

which can also be written as

```
list_of_numbers = [1, 5, 10, 100]
def sum(x, y):
return x + y
reduce(sum, list_of_numbers)
```

Bonus: Python provides this functionality in the built-in `sum`

function. This is the most readable expression imo.

```
list_of_numbers = [1, 5, 10, 100]
sum(list_of_numbers)
```