skip last line in loops

[eight02645999]

hi,
how can i skip printing the last line using loops (for /while)

eg

for line in open("file):
print line.

I want to skip printing last line of the file.thanks

 

[James Stroud]

hi,
how can i skip printing the last line using loops (for /while)

eg

for line in open("file):
print line.

I want to skip printing last line of the file.thanks

afile = open(filename)

xlines = afile.xreadlines()

aline = xlines.next
for nextline in xlines:
print aline
aline = nextline

James

 

[James Stroud]

afile = open(filename)

xlines = afile.xreadlines()

aline = xlines.next
for nextline in xlines:
print aline
aline = nextline

James

Shoule be

aline = xlines.next()

 

[tac-tics]

Try:
afile = open(filename)
lines = afile.readlines()[:-1] # assigns all except the last element to
a list "lines"
for line in lines:
print line

 

[Fredrik Lundh]

how can i skip printing the last line using loops (for /while)

eg

for line in open("file):
print line.

I want to skip printing last line of the file.

do it lazily:

last_line = None
for line in open("file):
if last_line:
print last_line
last_line = line

or just gobble up the entire file, and slice off the last item:

for line in list(open("file"))[:-1]:
print line

</F>

 

[eight02645999]

how can i skip printing the last line using loops (for /while)

eg

for line in open("file):
print line.

I want to skip printing last line of the file.

do it lazily:

last_line = None
for line in open("file):
if last_line:
print last_line
last_line = line

or just gobble up the entire file, and slice off the last item:

for line in list(open("file"))[:-1]:
print line

</F>

hi
would it be a problem with these methods if the file is like 20Gb in
size...?

 

[Roberto Bonvallet]

do it lazily:

last_line = None
for line in open("file):
if last_line:
print last_line
last_line = line

or just gobble up the entire file, and slice off the last item:

for line in list(open("file"))[:-1]:
print line

</F>

hi
would it be a problem with these methods if the file is like 20Gb in
size...?

The second one would be a problem, since it creates a list containing all
the lines of the file. Use the lazy approach.

 

[James Stroud]

how can i skip printing the last line using loops (for /while)

eg

for line in open("file):
print line.

I want to skip printing last line of the file.

do it lazily:

last_line = None
for line in open("file):
if last_line:
print last_line
last_line = line

or just gobble up the entire file, and slice off the last item:

for line in list(open("file"))[:-1]:
print line

</F>

hi
would it be a problem with these methods if the file is like 20Gb in
size...?

See the documentation for xreadlines.

James

 

[Fredrik Lundh]

See the documentation for xreadlines.

why?

</F>

 

[Paul Rubin]

for line in open("file):
print line.

I want to skip printing last line of the file.thanks

def all_but_last(it): # yield all but last item of an iterator
a = it.next()
for b in it:
yield a
a = b

for line in all_but_last(open("file")):
print line

 

[Daniel Klein]

hi,
how can i skip printing the last line using loops (for /while)

eg

for line in open("file):
print line.

I want to skip printing last line of the file.thanks

while True:
line1 = myfile.readline()
if not line1: break
line2 = myfile.readline()
if line2:
print line1
else:
break


Dan

 

[Fredrik Lundh]

do it lazily:

last_line = None
for line in open("file):
if last_line:
print last_line
last_line = line

or just gobble up the entire file, and slice off the last item:

for line in list(open("file"))[:-1]:
print line

</F>

>
would it be a problem with these methods if the file is like 20Gb in
size...?

not with the lazy version, of course. the "gobble up" version will
load the entire file into memory.

but cutting off a single line from a 20 gigabyte file by looping over
it sounds like a bit contrived, really. if you're really doing this
(why?), maybe you should just truncate the file in place instead.

</F>

 

[James Stroud]

why?

</F>

5.16 xreadlines -- Efficient iteration over a file

 

[Peter Otten]

5.16 xreadlines -- Efficient iteration over a file

http://www.python.org/dev/peps/pep-0004/

The cheat sheet for the effbot quiz

Peter

 

[stdazi]

lines = open('blah').readlines()
for i in range(0, len(lines)-1) :
print lines

 

[tobiah]

See the documentation for xreadlines.

James

Hmm...

This method returns the same thing as iter(f). New in version 2.1.
Deprecated since release 2.3. Use "for line in file" instead.