A little disappointed so far

[Robin Munn]

Graham Nicholls <graham at rockcons.co.uk> wrote:
> Steven Taschuk wrote:
> 
>> Quoth Graham Nicholls:
>>   [...]
>> 
>>> My tabstops are set to 2 in vi - thats what I like - sorry that the
>>> editor has expanded the m out to 8 .
>> 
>> Fwiw, the dominant convention for Python code is to indent by four
>> spaces and eschew the tab character.
>> 
> Hmmm again! I like my tabs.

And as long as you don't *ever* mix tabs and spaces, you should be fine.
But be aware that the Python interpreter considers that tabstops are set
every eight (8) characters -- see the second paragraph of:

    http://www.python.org/doc/current/ref/indentation.html

Therefore, if you use 2-character tabstops, or any number other than 8,
you should be aware that what you are seeing in your editor, and what
the Python interpreter is seeing, are two very different things. This
*will* bite you eventually if you don't pay very close attention. For
example, let's say you downloaded some Python code and are editing it.

# Some sample Python code using 4-space indents
for i in range(10):
    print i, i*i
print "All done!"

Now you decide to change this code to use a well-named temporary
variable to store the result of the calculation. So you move the cursor
to the "for" line and hit o to insert a new line. You then indent to the
proper level (as it looks to you on your screen) by pressing TAB twice.
What you see (TAB characters, normally invisible, I have represented by
>___ below):

# Some sample Python code using 4-space indents
for i in range(10):
>_>_square = i*i
    print i, square
print "All done!"

What the Python interpreter sees:

# Some sample Python code using 4-space indents
for i in range(10):
>_______>_______square = i*i
    print i, square
print "All done!"

The result is an IndentationError when Python hits the "print i, square"
line. But in your editor, it looks fine! This could cause you a lot of
grief unless you understand what's happening.

There are two (well, three really, but one of them I wouldn't recommend)
ways of dealing with this problem:

1. Every time you want to use someone else's code, spend time changing
the indentation to consistently use 2-character tabs everywhere. This is
time-consuming and error-prone. Not recommended.

2. Set your tabstops to 8. Your code will suddenly look a lot more
spread out, but at least you won't hit unexpected IndentationErrors
anymore.

3. Start using space characters for indentation. You can still get the
"feel" of using tabs with the right editor options. In my .vimrc, for
example, I have the following options:
    set tabstop=8
    set shiftwidth=4
    set expandtab
    set smarttab
The "smarttab" option is the key here: it lets me hit the Tab key at the
start of a line to indent by (shiftwidth) characters. Disadvantages:
you're not using tabs; if that's important to you, you won't like this
method. Advantages: this actually "feels" like you're inserting Tabs,
but space characters are actually going into the file. And pressing the
Backspace key also dedents by the appropriate amount.

No, I am *not* going to get into a discussion of whether tabs or spaces
are better in source code. If you want to use tabs, go ahead. I'm just
trying to point out what you need to know if you're going to do so.

-- 
Robin Munn <rmunn at pobox.com>
http://www.rmunn.com/
PGP key ID: 0x6AFB6838    50FF 2478 CFFB 081A 8338  54F7 845D ACFD 6AFB 6838