[Courses] [python] Lesson 1: Hello world

[L.S. Miller]

I do have one complaint.  You weren't kidding when you said the lessons
would be short and easy.  I've never programmed at all before and was
inordinately thrilled by the results of the first lesson.  More!

On Sat, Jun 18, 2011 at 3:18 PM, Akkana Peck <akkana at shallowsky.com> wrote:

> About that homework question, print "Hello,", name
>
> Everybody gets a point for the first comma -- it's part of the string
> you're printing. Good job! I mean it -- a lot of people don't get that
> at first.
>
> Pretty much everybody knew that the second comma, being outside the
> string, was telling Python to do something. But what? A lot of you
> pretty much figured it out -- that it's to separate the objects
> you're passing to the print statement -- but here are the details.
>
> Python's print statement is a bit magical, with a special syntax of
> its own that's different from most of the language.
> (Python 3 changes that.)
> You can give print a long list of things separated by commas, like:
>
> print a, b, c, d, e
>
> and it will print each of them with spaces
> between them. So in my Hello example, the comma outside the quotes
> just means that you're printing two things -- the string "Hello,"
> and the name -- with a space in between them.
>
> You need the comma. You can't give print a list of things without
> commas, i.e. you can't say
>
> print a b c d e     # Wrong: Python will give you a syntax error
>
> Sharon asked if there's any way to print multiple things without a
> space between them. There is, but it's a little bit harder. Instead of
> print "Hello,", name
> you could say
> print "Hello, " + name
>
> A plus + will stick two strings together without any space between
> them. (Notice that I added the space inside the string.) In fact, Kay
> suggested this:
> print "Hello, " + name + "!"
> which adds an exclamation mark at the end, with no space before it.
>
> You can mix commas and + as much as you want, but using + gets a little
> more complicated if your objects aren't all strings. For instance, you
> can say
> print "Today is lesson number", 1
> but you can't say
> print "Today is lesson number " + 1
> or Python will complain: cannot concatenate 'str' and 'int' objects
> In other words, + means something different for a string than for an
> integer number, and Python doesn't know what to do.
> So most of the time, using commas is easiest if you don't mind a space.
>
> Larry asked if the second comma was to prevent printing a newline.
> Not in this case, but commas can do that if you put them at the *end*
> of the print statement. Like this:
>
> print "Hello,", name,
>
> Peggy asked about double quotes vs. single quotes. In Python, you can
> use either type -- there's no difference. So use whichever type suits
> your own aesthetics. Some programmers prefer single quotes because
> they're easier to type (you don't need the shift key); some prefer
> double quotes because then you don't need to worry about apostrophes.
> For instance, "Python doesn't care which type you use" will work fine,
> whereas if you said 'Python doesn't care which type you use', you'd
> end up with a syntax error because the string would be 'Python doesn'
> and Python wouldn't know what to do with the rest of it.
>
> Of course, you have to end the string with the same type you used to
> start it. 'string" won't work.
>
> And on why the language is called Python: lots of people knew the
> answer, that it's named after Monty Python and not the snake. Though
> I love the "So O'Reilly could have a cool book cover" answer. :-)
>
> Darn, I think my followup was longer than the lesson! I hope I
> didn't miss anybody -- if you asked a question and I didn't answer
> it, or I wasn't clear enough, let me know.
>
>        ...Akkana
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