Kernel.Panic Kernel.Panic - 3 months ago 9
Python Question

How can I generate a list and flatten it the same time in python?

This is more of a refactoring question, as the code works as is. But since I am still learning

, I thought there would be a better way to do this, and I spent a few hours now digging into the other possibilities, but can't get anywhere.

So I have the following statement:

numbers = [re.split(' ?- ?', ticket.text.strip()) for ticket in tickets]

which obviously generates a list of lists. However, I want to have just a single list of the numbers taken out from that regex.

So this is the second line of code that flattens the above list (I found this solution here, on

flat = [item for setlist in numbers for item in setlist]

Main thing I am trying to achieve is to have this on 1 single line. Otherwise, I could of course have a normal
for .. in
loop, that would append each number to numbers list, but I like keeping it on 1 line.

If this is the best it can get, I would also love to know that please.. :)


You can achieve it using chain and map in single line as:

list(chain(*map(lambda x: re.split(' ?- ?', x.text.strip()), tickets)))


There is no need to use regex here, because you may achieve the same using split function of Python. Hence, your answer will become:

list(chain(*map(lambda x: x.text.replace(' ', '').split('-')), tickets)))


chain function from the itertools library is used to umwrap the list. Below is the sample example

>>> from itertools import chain
>>> my_nested_list = [[1,2,3], [4,5,6]]
>>> list(chain(*my_nested_list))
[1, 2, 3, 4, 5, 6]

Whereas map function is used to call the passed function (in this case lambda function) on each item of list.

>>> my_nested_list = [[1,2,3], [4,5,6]]
>>> map(lambda x: x[0], my_nested_list)
[1, 4]

And, split is used to split the content of string based on substring. For example:

>>> x = 'hey you - i am here'
>>> x.split('-')
['hey you ', ' i am here']  # Same answer as your regex