Question

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 1

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