Manually read lines in python

Question

I have a file that has the filename a new line, then the hashvalue of the file then a newline. This pattern repeats. Example:

blah.txt
23847EABF8742
file2.txt
1982834E387FA

I have a class called 'information' that has two member variables.

class information:
     filename=''
     hashvalue=''

Now I want to read in the file and store a filename and hashvalue in a new instance of an 'information' object and then push the instance of the information object onto a list.

The problem I am having is iterating over the file to read it. I want to read it line by line until the end of file. The problem with python's 'for line in file' method is that it grabs a line each time and I would be forced to do some kind of every other tactic to put the data in the correct member variable.

Instead, this is what I am trying to do...

list=[]
while(not end of file)
    x = information()
    x.filename = file.readline()
    x.hashvalue = file.readline()
    list.append(x)

Tom Hunt · Accepted Answer · 2015-02-20 22:45:31Z

2

You could write a generator function:

def twolines(file):
    cur = None
    for i in file:
        if cur is None:
            cur = i
        else:
            yield (cur, i)
            cur = None

Then pass your file object to twolines(), and do something like

for i, j in twolines(file):
    x = information()
    x.filename, x.hashvalue = i,j
    list.append(x)

answered Feb 20, 2015 at 22:45

Tom Hunt

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Comments

Joran Beasley · Accepted Answer · 2015-02-20 23:10:34Z

1

while True:
    x = information()
    x.filename = file.readline()
    if not x.filename:
       break
    x.hashvalue = file.readline()
    my_list.append(x)

maybe?

or

while True:
    x = information()
    try:
        x.filename = next(file)
        x.hashvalue = next(file)
    except StopIterationError:
        break
    my_list.append(x)

or my favorite

my_list = [filename,hashvalue for filename,hashvalue in zip(file,file)]

edited Feb 20, 2015 at 23:10

answered Feb 20, 2015 at 22:44

Joran Beasley

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Comments

RPBruiser · Accepted Answer · 2015-02-20 22:54:25Z

0

Another simple fix is by counting the lines. Introduce a variable like line = 0 for this. now you could try the following:

for lines in file:
    line = line + 1
    if line  % 2 == 1:
        # This will be the filename
    else:
        # This will be the hashcode

answered Feb 20, 2015 at 22:54

RPBruiser

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1 Comment

Joran Beasley Over a year ago

Im pretty sure he explicitly stated he didnt want to do that ... also for i,line in enumerate(file): if i%2 would probably be a minor improvement

Praveen Yalagandula · Accepted Answer · 2015-02-20 23:03:13Z

0

How about this:

list = [information(filename=x.rstrip(), hashvalue=next(it).rstrip()) for x in file]

edited Feb 20, 2015 at 23:03

answered Feb 20, 2015 at 22:51

Praveen Yalagandula

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3 Comments

Joran Beasley Over a year ago

file is already an iter ... you can just do for x in file.. and use next(file) instead of next(x)

Joran Beasley Over a year ago

it = iter(file.readlines()) is exactly identical to it=file

Joran Beasley Over a year ago

try and run it ... set file="A B C".split()

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