validatingCpp.py

__author__ = "streethacker"

#/usr/bin/python
#-*- coding:utf-8 -*-

# Data Structures and Algorithms Using Python
# CHAPTER 7: Stacks
# Listing 7.3: validatingCpp.py

from lliststack import Stack


def isValidSource(srcFile):
    """
    The function accepts a file object, which we assume was previously opened and contains C++
    source code.The file is scanned one line at a time and each line is scanned one character
    at a time to determine if it contains properly paired and balanced delimiters.
    """
    s = Stack()
    for line in srcFile:
        for token in line:
            if token in "{[(":
                # if token is one of the opening delimiters it should be pushed
                # into the stack.
                s.push(token)
            # if token is one of the closing delimiters it should be checke by
            # the following steps.
            elif token in ")]}":
                if s.isEmpty():
                    return False
                else:
                    left = s.pop()
                    if token == "}" and left != "{" or \
                            token == "]" and left != "[" or \
                            token == ")" and left != "(":
                        return False
    return s.isEmpty()

if __name__ == "__main__":
    with open("/home/streethacker/maxMsub/maxMsub.cpp", "r") as srcFile:
        if isValidSource(srcFile):
            print "This is a valid C++ file."
        else:
            print "This is an invalid C++ file, cause delimiters are not balanced."