how do I "peek" into the next line?

Jeffrey Maitland maitj at vianet.ca
Mon Dec 13 20:36:48 CET 2004


Jeffrey Maitland writes: 

> les_ander at yahoo.com writes:  
> 
>> Hi,
>> suppose I am reading lines from a file or stdin.
>> I want to just "peek" in to the next line, and if it starts
>> with a special character I want to break out of a for loop,
>> other wise I want to do readline().  
>> 
>> Is there a way to do this?
>> for example:
>> while 1:
>> line=stdin.peek_nextline()
>> if not line: break
>> if line[0]=="|":
>> break:
>> else:
>>     x=stdin.nextline()
>>     # do something with x  
>> 
>> thanks  
>> 
>> -- 
>> http://mail.python.org/mailman/listinfo/python-list
> 
> Well what you can do  is read the line regardless into a testing variable.  
> 
> here is some sample code (writting this off the topof my head so syntax 
> might be off some)  
> 
> import re  
> 
> file = open("test.txt", 'r')  
> 
> variablestr = '' #this would be your object.. in my example using a string 
> for the file data  
> 
> file.seek(0,2)
> eof = file.tell() #what this is the position of the end of the file.
> file.seek(0,0)  
> 
> while file.tell() != eof:
>    testline = file.readline()
>    if re.match("#", testline) == True:
>       break
>    else:
>       variablestr += testline  
> 
> file.close()  
> 
> now if I was concerned with being at the beging of the testline that it 
> read in  what you can do is in the if is something like:
> file.seek((file.tell() - len(testline)), 0)
> and that will move you back to the beginging of that line which is where 
> the readline from the previous call left you before the "peek".  
> 
> hope that helps some..  
> 
> Jeff
> -- 
> http://mail.python.org/mailman/listinfo/python-list

I noticed something in my code. 

re.match("#", testline) == True isn't possible it would be more like.
re.match("#", testline) != None 





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