I am using regular expressions to recognize the lines containing \begin{frame} in .tex files. Below is my code:
#!/usr/bin/python
import re,sys
def isEven(num):
res = [False,True][bool(num % 2 == 0)]
return res
textin = open(sys.argv[1]).readlines()
nline = 0
pat = r'\b\begin{frame}\b'
for line in textin:
line = line.strip(' ')
#print 'Test: ',line[:13]
if re.match(pat,line):
print 'here'
nline += 1
if isEven(nline):
print '%',line.strip('\n')
else:
print line.strip('\n')
This program aims to add the character '%' before the lines in the tex file if the number of frames is even. In other words, I want to comment the slides which the slide number is even.
Do you know what is the wrong in the pattern?
Look at your pattern string again:
r'\b\begin{frame}\b'
Notice it starts with '\b\b'. You mean the first one as a word boundary, the second one as part of what you want to match -- but how could re possibly guess what you mean each for?!
I don't think you need the word-boundaries, by the way -- in fact they may mess up the matching. Moreover, re.match only matches at the start; since you say "contain", as opposed to "start with", in your Q's text, you may actually want re.search.
To match a backslash, you need to double it in the pattern. And you can use a single backslash to escape punctuation, such as those braces.
So I would recommend...:
def isEven(n): return n%2 == 0
nline = 0
pat = r'\\begin\{frame\}'
with open(sys.argv[1]) as textin:
for line in textin:
line = line.strip()
if re.search(pat,line):
print 'here'
nline += 1
if isEven(nline):
print '%', line
else:
print line
I've done a few more improvements but they're not directly relevant to your Q (e.g, use with to open the file, and loop on it line by line; strip each line of whitespace completely, once, rather than by instalments; etc -- but you don't have to use any of these:-).