[Courses] [python] Lesson 6: Functions and dictionaries

[Akkana Peck]

Leslie writes:
> 	(1)  I would like to be able to put some text plus a variable in the
> raw_input string expression, but if I do that, the comma between them
> signals two arguments, whereas raw_input only expects one.
> 	For example,  I have randomly selected a key from my dictionary, and
> named it 'species’; now  I want to get the user’s response to this:
> “What is [species] nesting site?” and compare it to a value (nesting
> sites).  If I say x = raw_input (“What is”, species,”nesting site?”),
> raw_input doesn’t like that.  (I suspect there may be no fix but to
> print the variable in a separate statement.)

raw_input just takes a string, but Python has a great way of
formatting strings using variables ... I've been wanting to work
that into a lesson but haven't quite found the space, so I'm really
glad you asked.

Any time you're using a string, you can add formatting parameters to
it using % signs and a list of the variables. It looks like this:

x = raw_input("What is %s nesting site? " % (species))

Where you would normally put just a plain string, instead you put a
string with % specifiers inside it (called "format specifiers"),
followed by a single %, followed by a tuple containing the variables
to match the format specifiers.

Format specifiers have types: %s means insert a string into the
longer string (so if species = "blue footed booby", it would insert
that string where you put the %s). %d means an integer printed in
decimal format (you can also use %x for hexidecimal, %o for octal
etc.), %f means a floating point number. So you could say

print "There are %d birds at the %s nesting site" % ("booby", 572)

You can also do more complex formatting, like controlling how many
decimal places to show or printing in columns of a specific width.
Here are the gory details:
http://docs.python.org/library/stdtypes.html#string-formatting

> 	(2) Let’s suppose my keys are questions.  I randomly choose one and
> name it 'question’. I would like to use that for my raw_input expression
> (x = raw_input(question)) with a line return at the end, so that the
> user enters her response on the next line, not right on the same line as
> the question.  I was trying to use \n in various ways at the end of the
> raw_input statement but could not make it work.  Can I get a pointer on
> this?

Probably the easiest way is this:

raw_input(question + '\n')

passing raw_input a string that's your question string with a newline
added on to the end of it. Does that do what you need?

Nice work on the homework. I like your idea of matching any word,
but you're right that the logic of the code gets complicated fast.
I found the same thing.

There are some cleaner solutions, but they use Python features I
haven't talked about yet.  I'll wait until some more people have
tried the homework and see what other ideas come up before bringing
up some of the more advanced ways you might be able to use.

	...Akkana