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pythonformattingiterationlanguage-comparisons

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)

Solution

  • 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)