[Tutor] Re: %d

[Alan Gauld]

>In Alan Gauld's tutorial page 2 you suddenly move 
> from gentle hand holding to this:
>
>>>>print "The sum of %d and %d is: %d" % (v,w,x)


Not sure where you get page 2 from but in the 4th chapter we introduce that
notation as below:

-------------
>>>print 'The total is: ', 23+45

You've seen that we can print strings and numbers. Now we combine the two in
one print statement,
separating them with a comma. We can extend this feature by combining it with
a useful Python trick for
outputting data called a format string: 

>>> print "The sum of %d and %d is: %d" % (7,18,7+18)

In this command the format string contains '%' markers within it. The letter
'd' after the % tells Python
that a 'decimal number' should be placed there. The values to fill in the markers
are obtained from the
values inside the bracketed expression following the % sign on its own. 

There are other letters that can be placed after the % markers. Some of these
include: 

      %s - for string 
      %x - for hexadecimal number 
      %0.2f - for a real number with a maximum of 2 decimal places 
      %04d - pad the number out to 4 digits with 0's 

The Python documentation will give lots more... 

-----------------------

There then follows a chapter on data which introduces the concept of variables.
Then in the 6th chapter I use the line you quote above.... I recommend you read
the topics in order
using the master sitre at:

http://www.crosswinds.net/~agauld

or the zip/tgz files that you can download from there.

I do try to explain all concepts before using them!

Alan G.
>I thought % was for the modulus function.  

It is, but is also used for formatting.

> So what is that % doing in front of d which 
> I assume to be a built in variable?  

See the excerpt from simple seqiuences quoted above

>I've carried on through Alan's explanation of "for" 
> and "while".  This is easy to use 

You need to go back not forward, the explanation is 
in chapter 3...

>Sorry if this is a little less challenging than interfaces to
>Postgres...

Now I'm confusded, I've never written an interface 
to PostGres in my life! :-)

HTH,

Alan G