python constructor basic question

Question

I am trying to reuse an opened file which is declared inside the constructor instance of a class but I guess I am doing something logically wrong. For instance consider the following example

class Temp:
    def __init__(self):
        self.open_file_ = open('periodic_status','r')

    def function1(self):
        new_file = self.open_file_
        for i in new_file:
            print 'test1'

    def function2(self):
        for j in self.open_file_:
            print 'test2'

if __name__ == '__main__':
    obj1 = Temp()
    obj1.function1()
    obj1.function2()

In the above program I can print test1 but I am not able to print the statement test2. Can some one explain me the logic.

Thanks

Fredrik Pihl · Accepted Answer · 2011-05-24 22:10:59Z

3

Because your file handle has exhausted all the lines in the file. You need to rewind it in "function2" using:

f.seek(0)

to start over again

See here docs.python.org

answered May 24, 2011 at 22:10

Fredrik Pihl

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1 Comment

Tadeck Over a year ago

Ok, but how to check whether I exhausted all the lines in the file?

Ignacio Vazquez-Abrams · Accepted Answer · 2011-05-24 22:08:30Z

2

Copying the reference does not create a new iterator; the first round of iteration consumes the entire file, leaving none for the second. You'll need to seek back to the beginning if you want to read it again.

answered May 24, 2011 at 22:08

Ignacio Vazquez-Abrams

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1 Comment

Rkz Over a year ago

true, can you explain me how to seek back to the beginning of file.

Boaz Yaniv · Accepted Answer · 2011-05-24 22:11:51Z

1

You should add open_file_.seek(0) in the beginning of function to reset the file position to the beginning (its at the end of the file after reading it all in function1()).

answered May 24, 2011 at 22:11

Boaz Yaniv

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