Regular Expression for the special character "|" pipe

[Roy Smith]

In article <mailman.10370.1401191774.18130.python-list at python.org>,
 Wolfgang Maier <wolfgang.maier at biologie.uni-freiburg.de> wrote:

> On 27.05.2014 13:39, Aman Kashyap wrote:
> >> On 27.05.2014 14:09, Vlastimil Brom wrote:
> >>
> >>> you can just escpape the pipe with backlash like any other metacharacter:
> >>>
> >>> r"start=\|ID=ter54rt543d"
> >>>
> >>> be sure to use the raw string notation r"...", or you can double all
> >>
> >>> backslashes in the string.
> >>
> > Thanks for the response.
> >
> > I got the answer finally.
> >
> > This is the regular expression to be 
> > used:\\|ID=[a-z]*[0-9]*[a-z]*[0-9]*[a-z]*\\|
> >
> 
> or, and more readable:
> 
> r'\|ID=[a-z]*[0-9]*[a-z]*[0-9]*[a-z]*\|'
> 
> This is what Vlastimil was talking about. It saves you from having to 
> escape the backslashes.

Sometimes what I do, instead of using backslashes, I put the problem 
character into a character class by itself.  It's a matter of personal 
opinion which way is easier to read, but it certainly eliminates all the 
questions about "how many backslashes do I need?"

> r'[|]ID=[a-z]*[0-9]*[a-z]*[0-9]*[a-z]*[|]'

Another thing that can help make regexes easier to read is the VERBOSE 
flag.  Basically, it ignores whitespace inside the regex (see 
https://docs.python.org/2/library/re.html#module-contents for details).  
So, you can write something like:

pattern = re.compile(r'''[|]
                         ID=
                         [a-z]*
                         [0-9]*
                         [a-z]*
                         [0-9]*
                         [a-z]*
                         [|]''',
                     re.VERBOSE)

Or, alternatively, take advantage of the fact that Python concatenates 
adjacent string literals, and write it like this:

pattern = re.compile(r'[|]'
                     r'ID='
                     r'[a-z]*'
                     r'[0-9]*'
                     r'[a-z]*'
                     r'[0-9]*'
                     r'[a-z]*'
                     r'[|]'
                    )