Question about metacharacter '*'

rxjwg98 at gmail.com rxjwg98 at gmail.com
Mon Jul 7 20:51:02 CEST 2014


On Sunday, July 6, 2014 8:09:57 AM UTC-4, Devin Jeanpierre wrote:
> On Sun, Jul 6, 2014 at 4:51 AM,  <rxjwg98 at gmail.com> wrote:
> 
> > Hi,
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> >
> 
> > I just begin to learn Python. I do not see the usefulness of '*' in its
> 
> > description below:
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> >
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> >
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> >
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> >
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> > The first metacharacter for repeating things that we'll look at is *. * doesn't
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> > match the literal character *; instead, it specifies that the previous character
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> > can be matched zero or more times, instead of exactly once.
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> >
> 
> > For example, ca*t will match ct (0 a characters), cat (1 a), caaat (3 a
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> > characters), and so forth.
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> >
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> >
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> >
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> > It has to be used with other search constraints?
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> 
> 
> (BTW, this is a regexp question, not really a Python question per se.)
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> 
> 
> That's usually when it's useful, yeah. For example, [0-9] matches any
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> of the characters 0 through 9. So to match a natural number written in
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> decimal form, we might use the regexp [0-9][0-9]*, which matches the
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> strings "1", "12", and "007", but not "" or "Jeffrey".
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> 
> 
> Another useful one is `.*` -- `.` matches exactly one character, no
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> matter what that character is. So, `.*` matches any string at all.
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> 
> 
> The power of regexps stems from the ability to mix and match all of
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> the regexp pieces in pretty much any way you want.
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> 
> 
> -- Devin

Would you give me an example using your pattern: `.*` -- `.`?
I try it, but it cannot pass. (of course, I use it incorrectly)



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