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Re: Newbie: Check first two non-whitespace characters

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otaksoftspamtrap@gmail.com writes:

> I need to check a string over which I have no control for the first 2
> non-white space characters (which should be '[{').
>
> The string would ideally be: '[{...' but could also be something like 
> '  [  {  ....'.
>
> Best to use re and how? Something else?

No comment on whether re is good for your use case but another comment
on how. First, some test data:

  >>> data = '\r\n  {\r\n\t[ "etc" ]}\n\n\n')

Then the actual comment - there's a special regex type, \S, to match a
non-whitespace character, and a method to produce matches on demand:

  >>> black = re.compile(r'\S')
  >>> matches = re.finditer(black, data)

Then the demonstration. This accesses the first, then second, then third
match:

  >>> empty = re.match('', '')
  >>> next(matches, empty).group()
  '{'
  >>> next(matches, empty).group()
  '['
  >>> next(matches, empty).group()
  '"'

The empty match object provides an appropriate .group() when there is no
first or second (and so on) non-whitespace character in the data:

  >>> matches = re.finditer(black, '\r\t\n')
  >>> next(matches, empty).group()
  ''
  >>> next(matches, empty).group()
  ''

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Newbie: Check first two non-whitespace characters otaksoftspamtrap@gmail.com - 2015-12-31 10:18 -0800
  Re: Newbie: Check first two non-whitespace characters MRAB <python@mrabarnett.plus.com> - 2015-12-31 18:38 +0000
  Re: Newbie: Check first two non-whitespace characters Karim <kliateni@gmail.com> - 2015-12-31 19:54 +0100
  Re: Newbie: Check first two non-whitespace characters Karim <kliateni@gmail.com> - 2015-12-31 20:05 +0100
    Re: Newbie: Check first two non-whitespace characters cassius.fechter@gmail.com - 2015-12-31 11:21 -0800
  Re: Newbie: Check first two non-whitespace characters Cory Madden <csmadden@gmail.com> - 2015-12-31 10:56 -0800
  Re: Newbie: Check first two non-whitespace characters Denis McMahon <denismfmcmahon@gmail.com> - 2015-12-31 20:35 +0000
  Re: Newbie: Check first two non-whitespace characters Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-12-31 23:25 +0000
    Re: Newbie: Check first two non-whitespace characters Steven D'Aprano <steve@pearwood.info> - 2016-01-01 12:12 +1100
  Re: Newbie: Check first two non-whitespace characters Steven D'Aprano <steve@pearwood.info> - 2016-01-01 12:23 +1100
  Re: Newbie: Check first two non-whitespace characters Random832 <random832@fastmail.com> - 2015-12-31 20:31 -0500
  Re: Newbie: Check first two non-whitespace characters Jussi Piitulainen <harvesting@is.invalid> - 2016-01-01 10:16 +0200
  Re: Newbie: Check first two non-whitespace characters Karim <kliateni@gmail.com> - 2016-01-01 10:43 +0100

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