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copied!<ol> <li>Just extract all the interesting symbols from a line. </li> <li>Push the opening symbols onto stack and pop from the stack whenever you get a closing symbol. </li> <li>If the stack is clean, the symbols are balanced. If the stack underflows or doesn't get fully unwound you have unbalanced line. </li> </ol> <p>Sample code for checking a line follows - I've inserted a stray bracket into the first line.</p> <pre><code>d = """SL ID=0X14429A0B TY=STANDARD OWN=0X429A(03 EXT=22 SLTK=0X1C429A0B MP=0X684003F0 SUB=0X24400007 RT ID=0X18429A19 TY=CALONSC OWN=0X14429A0B EXLP=0X14429A0C CMDS=(N:0X8429A04,C:0X14429A0B) SGCC=2 REL=1 DESC="AURANT YD-INDSTRY LD" ATIS=T RT ID=0X18429A1A TY=CALONSC OWN=0X14429A0B EXLP=0X14429A08 CMDS=(R:0X8429A04,N:0X8429A05,C:0X14429A0B) SGCC=2 REL=2 DESC="AURANT YD TO TRK.1" ATIS=T RT ID=0X18429A1B TY=CALONSC OWN=0X14429A0B EXLP=0X14429A0A CMDS=(R:0X8429A04,R:0X8429A05,C:0X14429A0B) SGCC=2 REL=3 DESC="AURANT YD TO TRK.2" ATIS=T SL ID=0X14429A0C TY=STANDARD OWN=0X429A03 EXT=24 SLTK=0X1C429A0B MP=0X684003F1 SUB=0X24400007 RT ID=0X18429A1C TY=CALONSC OWN=0X14429A0C EXLP=0X14429A0B CMDS=(N:0X8429A04,C:0X14429A0C) SGCC=2 REL=1 DESC="AURANT YD-INDSTRY LD" ATIS=T TK ID=0X1C429A08 TY=BLKTK OWN=0X429A03 EXT=12 LRMP=0X6C40BDAF LEN=5837 FSPD=60 PSPD=65 QUAL=TRK.1 MAXGE=0 MAXGW=0 JAL=4 ALT=12 SUB=0X24400007 RULES=(CTC:B:UP:0X24400007:485.7305:486.8359:T) LLON=-118.1766772 RLON=-118.1620059 LLAT=34.06838375 RLAT=34.07811764 LELE=416.6983 RELE=425.0596 ULAD=NO URAD=NO PT ID=0X20429A0F TY=STANDARD OWN=0X1C429A08 LTK=0X1C40006C RTK=0X1C429A0C REL=1 LEN=1 LQUAL="TRK.1" RQUAL="TRK.1" PTK OWN=0X1C429A08 PID=0X1C429A13""" def unbalanced(line): close_symbols = {'"' : '"', '(': ")", '[': ']', "'" : "'"} syms = [x for x in line if x in '\'"[]()'] stack = [] for s in syms: try: if len(stack) > 0 and s == close_symbols[stack[-1]]: stack.pop() else: stack.append(s) except: # catches stack underflow or closing symbol lookup return True return len(stack) != 0 print unbalanced("hello 'there' () []") print unbalanced("hello 'there\"' () []") print unbalanced("][") lines = d.splitlines() # in your case you can do open("file.txt").readlines() print [line for line in lines if unbalanced(line)] </code></pre> <p>For large files, you don't want to read all the files into memory so use fragment like this instead:</p> <pre><code>with open("file.txt") as infile: for line in infile: if unbalanced(line): print line </code></pre>

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