What do [] brackets in a for loop in python mean?

Question

I'm parsing JSON objects and found this sample line of code which I kind of understand but would appreciate a more detailed explanation of:

for record in [x for x in records.split("\n") if x.strip() != '']:

I know it is spliting records to get individual records by the new line character however I was wondering why it looks so complicated? is it a case that we can't have something like this:

for record in records.split("\n") if x.strip() != '']:

So what do the brackets do []? and why do we have x twice in x for x in records.split....

Thanks

Answer 1

The "brackets" in your example constructs a new list from an old one, this is called list comprehension.

The basic idea with [f(x) for x in xs if condition] is:

def list_comprehension(xs):
    result = []
    for x in xs:
        if condition:
            result.append(f(x))
    return result

The f(x) can be any expression, containing x or not.

Answer 2

That's a list comprehension, a neat way of creating lists with certain conditions on the fly.

You can make it a short form of this:

a = []
for record in records.split("\n"):
    if record.strip() != '':
        a.append(record)

for record in a:
    # do something