Lookahead while doing: for line in fh.readlines():
Veek. M
vek.m1234 at gmail.com
Fri Mar 4 08:04:04 EST 2016
Terry Reedy wrote:
> On 2/27/2016 4:39 AM, Veek. M wrote:
>> I want to do something like:
>>
>> #!/usr/bin/env python3
>>
>> fh = open('/etc/motd')
>> for line in fh.readlines():
>> print(fh.tell())
>>
>> why doesn't this work as expected.. fh.readlines() should return a
>> generator object and fh.tell() ought to start at 0 first.
>
> Not after you have already read some data. Readlines() reads the
> entire
> file and splits it into lines. readline reads at least a single
> block.
> Reading a single byte or character at a time looking for /n would be
> too slow, so even after readline, the file pointer will be somewhere
> past the end of the last line returned.
>
>> Instead i get the final count repeated for the number of lines.
>>
>> What i'm trying to do is lookahead:
>> #!whatever
>>
>> fh = open(whatever)
>> for line in fh.readlines():
>> x = fh.tell()
>> temp = fh.readline()
>> fh.seek(x)
>>
>
>
I get that readlines() would slurp the whole file for efficiency
reasons. Why doesn't fh.seek() work though. Object 'fh' is a data
structure for the OS file descriptor similar to FILE in C.
<class '_io.TextIOWrapper'>
So if seek works in C, how come it doesn't work in python wrt
readlines() which is just a method. What obviates the functioning of
seek wrt readlines()?
fh.tell() works at the line level.. and fh.readline() works with
fh.seek(0)
More information about the Python-list
mailing list