Writelines() a bit confusing

[aiwarrior]

If file.WriteLines( seq ) accepts a list and it says it writes lines,
why does it write the whole list in a single line. Be cause of that
the reverse of file.writelines(seq) is not file.readlines().
Are the assumptions i made correct? If yes why is this so?

I find a function called writelines not actualy writing the list in
lines wierd.

something = ['re','ri','ro']
f.writelines( something )
something_else = f.readlines()

In this case the list something_else will be diffrent from something

 

[Stefan Sonnenberg-Carstens]

If file.WriteLines( seq ) accepts a list and it says it writes lines,
why does it write the whole list in a single line. Be cause of that
the reverse of file.writelines(seq) is not file.readlines().
Are the assumptions i made correct? If yes why is this so?

I find a function called writelines not actualy writing the list in
lines wierd.

something = ['re','ri','ro']
f.writelines( something )
something_else = f.readlines()

In this case the list something_else will be diffrent from something

Please see this:

Help on built-in function writelines:

writelines(...)
writelines(sequence_of_strings) -> None. Write the strings to the file.

Note that newlines are not added. The sequence can be any iterable
object
producing strings. This is equivalent to calling write() for each
string.

so you'd want this:

f.writelines([x+os.linesep for x in strings])

or something similar.

Why ? Ask the originator of this function.
One explanation:
If you do this:

f1 = file('file1')
f2 = file('file2','w')
f2.writelines(f1.readlines())
f1.close() ; f2.close()

all is how it should be.

 

[Steve Holden]

If file.WriteLines( seq ) accepts a list and it says it writes lines,
why does it write the whole list in a single line. Be cause of that
the reverse of file.writelines(seq) is not file.readlines().
Are the assumptions i made correct? If yes why is this so?

I find a function called writelines not actualy writing the list in
lines wierd.

something = ['re','ri','ro']
f.writelines( something )
something_else = f.readlines()

In this case the list something_else will be diffrent from something

Your list is *not* what you would get in from a call to readlines.

Try it.

regards
Steve
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[Gre7g Luterman]

If file.WriteLines( seq ) accepts a list and it says it writes lines,
why does it write the whole list in a single line. Be cause of that
the reverse of file.writelines(seq) is not file.readlines().
Are the assumptions i made correct? If yes why is this so?

readlines() and writelines() are complimentary. readlines() leaves the line
terminators intact. It does not strip them off. writelines() does not add in
carriage returns for the same reason. For example:

D=open("temp.txt").readlines()
D ['the quick\n', 'brown fox\n', 'jumps over\n', 'the lazy dog.']
open("temp2.txt","w").writelines(D)

will create temp2.txt to be identical to temp.txt.

 

[aiwarrior]

If file.WriteLines( seq ) accepts a list and it says it writes lines,
why does it write the whole list in a single line. Be cause of that
the reverse of file.writelines(seq) is not file.readlines().
Are the assumptions i made correct? If yes why is this so?

readlines() and writelines() are complimentary. readlines() leaves the line
terminators intact. It does not strip them off. writelines() does not add in
carriage returns for the same reason. For example:

['the quick\n', 'brown fox\n', 'jumps over\n', 'the lazy dog.']

will create temp2.txt to be identical to temp.txt.

I Haven't seen that way before thanks, both of you

 

[Gabriel Genellina]

En Sat, 19 May 2007 10:31:50 -0300, Stefan Sonnenberg-Carstens

so you'd want this:

f.writelines([x+os.linesep for x in strings])

or something similar.

You would use os.linesep *only* if the file was opened in binary mode -
unusual if you want to write lines of text.
For a file opened in text mode (the default) the line terminator is always
'\n' - let Python handle the platform differences. On Windows you would
end with malformed or duplicate line terminators if you use explicitely
os.linesep when writing.
See http://mail.python.org/pipermail/python-list/2000-May/037191.html