Question

I have a pattern:
“\nvariable WORD”

This pattern shows up a lot of times in the string and I want a list of indexes that this pattern shows up at. “WORD” is fixed, and doesn’t change from instance to instance, but “variable” varies in content and length.

In python, I know this matches all WORD and returns their indices in a list:

contents="some long string"
print [m.start() for m in re.finditer('WORD',contents)]

So in short, how do I find indices of all “variable” after \n but before “WORD”?

Answer 1

If the only tool you know is a hammer, every problem looks like a nail.

Regular expressions are powerful hammers, but sometimes not the best tool for the task in hand. In fact, regular expressions are abused a lot, I feel shivers down the spine every time someone asks me to check complex regular expressions from other programmer (often I’m unable understand mine after a few weeks).

On the other side, EBNF (Extended Backus–Naur Form) notation is a lot easier to understand and maintain.

from simpleparse.parser import Parser

grammar = r"""
<space>      := [ \t]
<newline>    := '\n'
<identifier> := [A-Za-z_],[A-Za-z0-9z_]*
match        := newline,identifier,space+,'WORD'
<junk>       := newline*,identifier,space+,-'WORD',(identifier/space)*
data         := (match/junk)*
"""

parser = Parser(grammar, 'data')

data = 'some junk\nvariable1 WORD\nvariable2 some ' +\
       'junk\nvariable3 WORD\nvariable4 some other ' +\
       'junk\nvariable5 WORD'

(start, matches, stop) = parser.parse(data)

print [ start for name, start, stop, other in matches ]

This will print:

[9, 44, 85]