Andrei wrote:
> Dick Moores wrote:
>
>> I've been trying to learn new things from the Cookbook, but here's a
>> recipe the utility of which I don't understand at all. Why interpolation
>> (whether the ruby way or not)? Maybe a better example than the couple
>> given would help me?
>>
> <snip>
>
> Normal string formatting in Python works by including in the string a
> sort of type definition (e.g. '%s' means 'insert a string here', '%d' is
> 'insert an integer here', etc.). You have to supply the arguments
> after the format string, in a tuple. For example:
>
> >>> print 'Name: %s\nAge: %d' % (username, userage)
> Name: John Doe
> Age: 39
>
> With the recipe provided, you can put the variables you want inserted
> directly in the format string - it's no longer necessary to append them
> in a tuple. So for the example above, it would become:
>
> >>> print interp('Name: #{username}\nAge: #{userage}')
>
This accomplishes nearly the same thing:
>>> d = {'username':'bob','userage':23}
>>> print "Name: %(username)s, Age: %(userage)s" % d
Name: bob, Age: 23
The only difference is that the items have to be keys in the dictionary,
instead of just variables,
but that's not necessarily a disadvantage.
But I understand they're trying to emulate it exactly as it operates in
other languages.
>
> The recipe has some disadvantages:
>
> - you have put your variable names in a string. This is bad practice -
> if you rename variables, it's easy to overlook them in strings.
>
This is a disadvantage in the dictionary method too, it seems.
> - format strings can be used to translate an application. You just give
> the translator your 'Name: %s' string and he gives you 'Borkbork: %s' or
> whatever. The translation doesn't need to be modified if you decide to
> make a user class and get rid of the username and userage vars.
>
I don't see what you mean here. The string in the example,
interp('Name: #{username}\nAge: #{userage}')
could be translated too.
> - format strings give you more control, so you can e.g. specify how many
> digits a float should have when formatted.
The dictionary method would allow you this control.
HTH,
-Luke
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