How to write a regular expression to match a string literal where the escape is a doubling of the quote character?

python regex fortran ply
Brendan picture Brendan · Jan 26, 2010 · Viewed 8.7k times · Source

I am writing a parser using ply that needs to identify FORTRAN string literals. These are quoted with single quotes with the escape character being doubled single quotes. i.e.

'I don''t understand what you mean'

is a valid escaped FORTRAN string.

Ply takes input in regular expression. My attempt so far does not work and I don't understand why.

t_STRING_LITERAL = r"'[^('')]*'"

Any ideas?

Answer

Anon. picture Anon. · Jan 26, 2010

A string literal is:

  1. An open single-quote, followed by:
  2. Any number of doubled-single-quotes and non-single-quotes, then
  3. A close single quote.

Thus, our regex is:

r"'(''|[^'])*'"

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