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pythonformattingiterationlanguage-comparisons
Wayne Werner
Wayne Werner

Reputation: 51857

Iterate a format string over a list

In Lisp, you can have something like this:

(setf my-stuff '(1 2 "Foo" 34 42 "Ni" 12 14 "Blue"))
(format t "~{~d ~r ~s~%~}" my-stuff)

What would be the most Pythonic way to iterate over that same list? The first thing that comes to mind is:

mystuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]
for x in xrange(0, len(mystuff)-1, 3):
    print "%d %d %s" % tuple(mystuff[x:x+3])

But that just feels awkward to me. I'm sure there's a better way?

Well, unless someone later provides a better example, I think gnibbler's solution is the nicest\closest, though it may not be quite as apparent at first how it does what it does:

mystuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]
for x in zip(*[iter(mystuff)]*3):
    print "{0} {1} {2}".format(*x)

Upvotes: 11

Views: 25505

Answers (6)

eyquem
eyquem

Reputation: 27585

stuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]

it = iter(stuff)
itn = it.next

print '\n'.join("%d %d %s" % (el,itn(),itn())
                for el in it)

Very understandable, I think

Upvotes: 2

ksed
ksed

Reputation: 375

A two liner based on Wright:

mystuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]
print '\n'.join("{0},{1},{2}".format(*mystuff[x:x+3]) for x in xrange(0, len(mystuff)-1, 3))

Upvotes: 0

Walter Mundt
Walter Mundt

Reputation: 25271

I'd say the most Pythonic would be to make the list deeper:

mystuff = [(1, 2, "Foo"), (34, 42, "Ni"), (12, 14, "Blue")]
for triplet in mystuff:
    print "%d %d %s" % triplet

Upvotes: 3

John La Rooy
John La Rooy

Reputation: 304355

mystuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]
for x in zip(*[iter(mystuff)]*3):
    print "%d %d %s"%x

Or using .format

mystuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]
for x in zip(*[iter(mystuff)]*3):
    print "{0} {1} {2}".format(*x)

If the format string is not hardcoded, you can parse it to work out how many terms per line

from string import Formatter
num_terms = sum(1 for x in Formatter().parse("{0} {1} {2}"))

Putting it all together gives

mystuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]
fmt = "{0} {1} {2}"
num_terms = sum(1 for x in Formatter().parse(fmt))
for x in zip(*[iter(mystuff)]*num_terms):
    print fmt.format(*x)

Upvotes: 13

Ken
Ken

Reputation: 10611

I think join is the most similar feature in Python:

(format t "~{~D, ~}" foo)

print(foo.join(", "))

It's a little worse when you have multiple items inside, as you see, though if you have a group-by function (which is really useful anyway!), I think you can make it work without too much trouble. Something like:

mystuff = [1, 2, "Foo", 34, 42, "Ni", 12, 14, "Blue"]
print(["%d %d %s" % x for x in group(mystuff, 3)].join("\n"))

Upvotes: 6

Josh Wright
Josh Wright

Reputation: 2505

For starters, I'd use the newer string formatting methods in 2.6+

print "{0} {1} {2}".format(*mystuff[x:x+3])

Upvotes: 4

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