[Tutor] Example for read and readlines()

[Asad]

Hi All,

          thanks for the reply so to put into context say I have a file
logfile formatted in text lines

1)           and I want to extract the start time , error number and end
time from this logfile so in this case what should I use I guess option 1  :

with open(filename, 'r') as f:
    for line in f:
        process(line)

should be fine or any other option ?

2) Another case is a text formatted logfile and I want to print (n-4)
lines n is the line where error condition was encountered .

3) Do we need to ensure that each line in the logfile ends with \n .

    \n is not visible so can we verify in someway to proof EOL \n is placed
in the file .


Thanks,




>
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>
>
>
> ---------- Forwarded message ----------
> From: Asad <asad.hasan2004 at gmail.com>
> To: tutor at python.org
> Cc:
> Bcc:
> Date: Sun, 11 Nov 2018 12:19:36 +0530
> Subject: [Tutor] Example for read and readlines()
> Hi All ,
>
>          If I am loading a logfile what should I use from the option 1,2,3
>
> f3 = open ( r"/a/b/c/d/test/test_2814__2018_10_05_12_12_45/logA.log", 'r' )
>
> 1) should only iterate over f3
>
> 2) st = f3.read()
> Should iterate over st
>
>
> 3) st1 = f3.readlines()
>
> Should iterate over st1
>
> How are the above options different it they are not can there be some
> examples to describe in which situations should we each method .
>
>
> Thanks,
>
> --
> Asad Hasan
> +91 9582111698
>
>
>
>
> ---------- Forwarded message ----------
> From: "Steven D'Aprano" <steve at pearwood.info>
> To: tutor at python.org
> Cc:
> Bcc:
> Date: Sun, 11 Nov 2018 20:40:49 +1100
> Subject: Re: [Tutor] Example for read and readlines()
> On Sun, Nov 11, 2018 at 12:19:36PM +0530, Asad wrote:
> > Hi All ,
> >
> >          If I am loading a logfile what should I use from the option
> 1,2,3
>
> Depends what you want to do. I assume that the log file is formatted
> into lines of text, so you probably want to iterate over each line.
>
> with open(filename, 'r') as f:
>     for line in f:
>         process(line)
>
> is the best idiom to use for line-by-line iteration. It only reads each
> line as needed, not all at once, so it can handle huge files even if the
> file is bigger than the memory you have.
>
>
> > f3 = open ( r"/a/b/c/d/test/test_2814__2018_10_05_12_12_45/logA.log",
> 'r' )
>
> Don't use raw strings r"..." for pathnames.
>
>
> > 1) should only iterate over f3
> >
> > 2) st = f3.read()
>
> Use this if you want to iterate over the file character by character,
> after reading the entire file into memory at once.
>
>
> > 3) st1 = f3.readlines()
>
> Use this if you want to read all the lines into memory at once.
>
>
>
> --
> Steve
>
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>


-- 
Asad Hasan
+91 9582111698