Ray Parrish wrote:
Ethan Furman wrote:
[email protected] wrote:
[snippety]
with open(outfilename,'w') as outfile:
outfile.write(header)
for line in data4:
line.replace('[',' ').replace(']',' ')
outfile.write(line)
for line in data4:
outfile.write(','.join([str(item) for item in line]))
~Ethan~
Hello,
Sorry to jump in here, but I am fairly new to Python programming, and
the syntax you are using in your answer is intriguing me. I missed the
question, as I just joined this group last night.
Welcome to the group!
Could you please explain to me what the ','.join() is doing in your
write command?
The .join() is a method of string objects. It is used to join together
a list of strings into a new string. For example, if you have the list
--> example = ['this', 'is', 'a', 'list']
then
--> ' '.join(example)
'this is a list'
--> '-'.join(example)
'this-is-a-list'
--> ' * - * '.join(example)
'this * - * is * - * a * - * list'
As you can see, whatever your seperator string is, it gets inserted in
between each list element to make the new string.
I understand the code for the loop above, but it is new to me, so if
there is a mistake in it, that the question was about, I would
appreciate being informed of what I missed to facilitate my ultimate
understanding of the with construct, which I am pretty shaky on so far.
The mistake in the original code was the line.replace() -- at that
point, line is a row from an array which has no replace method, so the
code errors out. The fix is to take the the row, convert it into a
string, and then go from there. My preference for doing that is usually
--> ','.join(['%s' % item for item in line])
as using the % formating gives plenty of flexibility.
The 'with' statement is standard in Python 2.6. In 2.5 you have to have
the statement 'from __future__ import with_statement' at the top of your
module. Basically, it allows you take code like this:
--> text_file = open('/some/path/and/file.txt', 'w')
--> try:
--> for something in a_big_data_object:
--> text_file.write(something.process())
--> finally:
--> text_file.close()
and replace it with code like this:
--> with open('/some/path/and/file.txt', 'w') as text_file:
--> for something in a_big_data_object:
--> text_file.write(something.process())
and when the loop is done, exception or no, text_file gets closed. Of
course, the real fun begins when you write your own context managers for
use with the 'with' statement.
Thanks, Ray Parrish
You are welcome.
~Ethan~
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