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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

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  • It's a list comprehension, see related: stackoverflow.com/questions/16341775/… Commented Jun 5, 2015 at 15:26
  • EdChum is right (duh); note that it doesn't have to do with loops in particular. This notation is a terse way to create lists. A loop can iterate also over lists. Commented Jun 5, 2015 at 15:28
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    Thanks for both of you inputs, on a side note people love down voting question on here. If you're going to vote a question down then I think you should leave a comment saying why. I think it's a valid programming question which I couldn't find anywhere else or know how to search for. Commented Jun 5, 2015 at 15:38
  • @Mo. see: stackoverflow.com/questions/38229059/… Commented Mar 8, 2017 at 13:24

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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.

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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
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