read files

[J. Peng]

first I know this is the correct method to read and print a file:

fd = open("/etc/sysctl.conf")
done=0
while not done:
line = fd.readline()
if line == '':
done = 1
else:
print line,

fd.close()
I dont like that flag of "done",then I tried to re-write it as:

fd = open("/etc/sysctl.conf")
while line = fd.readline():
print line,
fd.close()
this can't work.why?

[Mel]

J. Peng wrote:

first I know this is the correct method to read and print a file:

fd = open("/etc/sysctl.conf")
done=0
while not done:
line = fd.readline()
if line == '':
done = 1
else:
print line,

fd.close()
I dont like that flag of "done",then I tried to re-write it as:

fd = open("/etc/sysctl.conf")
while line = fd.readline():
print line,
fd.close()
this can't work.why?

Formally, because line = fd.readline() is a statement, not an
expression, and it can't be put into an if statement like that.

The most idiomatic way is probably
fd = open ("/etc/sysctl.conf")
for line in fd:
print line

Mel.

[Benjamin]

On Jan 21, 9:08 pm, Mel <[e-mail]:

J. Peng wrote:

first I know this is the correct method to read and print a file:

fd = open("/etc/sysctl.conf")
done=0
while not done:
line = fd.readline()
if line == '':
done = 1
else:
print line,

fd.close()

I dont like that flag of "done",then I tried to re-write it as:

fd = open("/etc/sysctl.conf")
while line = fd.readline():
print line,
fd.close()

this can't work.why?

Formally, because line = fd.readline() is a statement, not an
expression, and it can't be put into an if statement like that.

The most idiomatic way is probably

fd = open ("/etc/sysctl.conf")
for line in fd:
print line

more idiomatic in Python 2.5+:

from __future__ import with_statement
with open("/my/file.conf") as fd:
for line in fd:
print line

>
Mel.

[Steven D'Aprano]

On Tue, 22 Jan 2008 11:00:53 +0800, J. Peng wrote:

first I know this is the correct method to read and print a file:

fd = open("/etc/sysctl.conf")
done=0
while not done:
line = fd.readline()
if line == '':
done = 1
else:
print line,

fd.close()

The evolution of a Python program.

# Solution 2:

fd = open("/etc/sysctl.conf")
done = False
while not done:
line = fd.readline()
if line:
print line,
else:
done = True
fd.close()

# Solution 3:

fd = open("/etc/sysctl.conf")
while True:
line = fd.readline()
if line:
print line,
else:
break
fd.close()
# Solution 4:

fd = open("/etc/sysctl.conf")
lines = fd.readlines()
for line in lines:
print line,
fd.close()
# Solution 5:

fd = open("/etc/sysctl.conf", "r")
for line in fd.readlines():
print line,
fd.close()
# Solution 6:

for line in open("/etc/sysctl.conf").readlines():
print line,
# garbage collector will close the file (eventually)
# Solution 7:

fd = open("/etc/sysctl.conf", "r")
line = fd.readline()
while line:
print line,
line = fd.readline()
fd.close()
# Solution 8:

fd = open("/etc/sysctl.conf", "r")
for line in fd:
print line,
fd.close()
# Solution 9:

for line in open("/etc/sysctl.conf"):
print line,
# Solution 10:
# (the paranoid developer)

try:
fd = open("/etc/sysctl.conf", "r")
except IOError, e:
log_error(e) # defined elsewhere
print "Can't open file, please try another."
else:
try:
for line in fd:
print line,
except Exception, e:
log_error(e)
print "Reading file was interrupted by an unexpected error."
try:
fd.close()
except IOError, e:
# Can't close a file??? That's BAD news.
log_error(e)
raise e


--
Steven

[J. Peng]

Thank you. That gave so much solutions.
And thanks all.
Steven D'Aprano 写�:

On Tue, 22 Jan 2008 11:00:53 +0800, J. Peng wrote:

>first I know this is the correct method to read and print a file:

fd = open("/etc/sysctl.conf")
done=0
while not done:
line = fd.readline()
if line == '':
done = 1
else:
print line,

fd.close()

The evolution of a Python program.

# Solution 2:

fd = open("/etc/sysctl.conf")
done = False
while not done:
line = fd.readline()
if line:
print line,
else:
done = True
fd.close()

# Solution 3:

fd = open("/etc/sysctl.conf")
while True:
line = fd.readline()
if line:
print line,
else:
break
fd.close()
# Solution 4:

fd = open("/etc/sysctl.conf")
lines = fd.readlines()
for line in lines:
print line,
fd.close()
# Solution 5:

fd = open("/etc/sysctl.conf", "r")
for line in fd.readlines():
print line,
fd.close()
# Solution 6:

for line in open("/etc/sysctl.conf").readlines():
print line,
# garbage collector will close the file (eventually)
# Solution 7:

fd = open("/etc/sysctl.conf", "r")
line = fd.readline()
while line:
print line,
line = fd.readline()
fd.close()
# Solution 8:

fd = open("/etc/sysctl.conf", "r")
for line in fd:
print line,
fd.close()
# Solution 9:

for line in open("/etc/sysctl.conf"):
print line,
# Solution 10:
# (the paranoid developer)

try:
fd = open("/etc/sysctl.conf", "r")
except IOError, e:
log_error(e) # defined elsewhere
print "Can't open file, please try another."
else:
try:
for line in fd:
print line,
except Exception, e:
log_error(e)
print "Reading file was interrupted by an unexpected error."
try:
fd.close()
except IOError, e:
# Can't close a file??? That's BAD news.
log_error(e)
raise e

[Gabriel Genellina]

En Tue, 22 Jan 2008 02:03:10 -0200, Paul Rubin
<"http://phr.cx"@NOSPAM.invalidescribió:

"J. Peng" <jp***@block.duxieweb.comwrites:

> print line,

Do you really want all the lines crunched together like that? If not,
leave off the comma.

Remember that Python *keeps* the end-of-line charater at the end of each
line; if you leave out the comma, you'll print them doubly spaced.

--
Gabriel Genellina

[J. Peng]

Gabriel Genellina 写�:

En Tue, 22 Jan 2008 02:03:10 -0200, Paul Rubin
<"http://phr.cx"@NOSPAM.invalidescribió:

>"J. Peng" <jp***@block.duxieweb.comwrites:

>> print line,

Do you really want all the lines crunched together like that? If not,
leave off the comma.

Remember that Python *keeps* the end-of-line charater at the end of each
line; if you leave out the comma, you'll print them doubly spaced.

Most languages (AFAIK) keep the newline character at the end of lines
when reading from a file.But python's difference is its 'print' built-in
function add a newline automatically for you. So without that ',' we
will get double newlines.