[Tutor] Writing to CSV string containing quote and comma

[Steven D'Aprano]

On Mon, Dec 09, 2013 at 11:14:38PM +0000, J Sutar wrote:

> Steven, I updated the very last line of code as below, as I need to get the
> word wrapped around quotes. Is that a good way of achieving that?
[...]
>     writer.writerow([str(n) + " " + chr(34) + s + chr(34) for n, s in
>                      zip(numbers, words)])


Not really a good way, no.

Python has two different quote characters ' and " so you can use one for 
delimiters and the other inside the string:

s = "this string contains ' single quote"
s = 'this string contains " double quote'

If you need both, you can escape the one that matches the delimiter:

s = 'this string contains both \' single and " double quotes'

Rather than assembling the final string piece by piece using string 
concatenation (the + operator), it is usually better to use template 
strings. Python has three standard ways to do template strings:

the % operator (like C's printf);

the format() method;

the string module's Template class.

I won't talk about the Template class, as it is fairly specialised and 
less convenient. Compare your version:

str(number) + " " + chr(34) + word + chr(34)

with the formatting versions:

'%d "%s"' % (number, word)

'{0} "{1}"'.format(number, word)


In Python 2.7, you can abbreviate that last one slightly:

'{} "{}"'.format(number, word)


Either should be preferred to building the string by hand with + signs. 
The rule of thumb I use is to say that adding two substrings together is 
fine, if I need more than one + sign I use a format string. So these 
would be okay:

plural = word + "s"
line = sentence + '\n'

but anything more complex and I would use % or format().



-- 
Steven