Regular Expression in Python

use

import re

You can use Regular Expression (module included in Python version 3x, read HOWTO here) to try writing regex. Here is a simple code that I tried yesterday. The code read the whole file line-by-line and try to split the line into individual word. Regex is used to capture the word and recognise separators. By default, split() separates words by space. We use regex "sep" to recognise 1) any character 2) parentheses 3) minus sign. Here is the code:

# read input file and separate words

      #   16 aug 2017

      

      import re

      

      sep = '[\s*()-]'

      

      def process(line):

          # e = line.split()

          # print(e)

          e = [x for x in re.compile(sep).split(line)]

          print(e)

          for w in e:

              if len(w) > 0: print(w)

      

      def readfile(filename):

          infile  = open(filename,'r')

          for line in infile:

              if line[-1] ==
      '\n':     # strip newline

                  line =
      line[:-1]

              print('>',line)

              process(line)

          infile.close()

      

      def main():

          readfile('fac.txt')

Here is the sample input file "fac.txt"

// fac.txt

      

      fac(n)

        if n == 0 return 1

        return n * fac(n-1)

      

      main()

        print(fac(6))

Play around with this piece of code and try to write different Regex to see how to match the different pattern.

last update 17 Aug 2017