I decided, that I learn a bit of Python. The first introduction says that it uses indentation to group statements. While the best habit is clearly to use just one of these what happens if I interchange them? How many spaces will be considered equal to one tab? Or will it fail to work at all if tabs and spaces are mixed?
A:
4 spaces are one tab ( in my setup ) but as far as i know, they are not intercahnged. you can use either spaces or tabs. not both.
Am
2010-01-09 18:59:05
Not necessarily. That depends on your setup.
Noufal Ibrahim
2010-01-09 19:00:49
+6
A:
Spaces are not treated as equivalent to tab. A line indented with a tab is at a different indentation from a line indented with 1, 2, 4 or 8 spaces.
Proof by counter-example (erroneous, or, at best, limited - tab != 4 spaces):
x = 1
if x == 1:
^Iprint "fff\n"
print "yyy\n"
The '^I' shows a TAB. When run through Python 2.5, I get the error:
File "xx.py", line 4
print "yyy\n"
^
IndentationError: unindent does not match any outer indentation level
Thus showing that in Python 2.5, tabs are not equal to spaces (and in particular not equal to 4 spaces).
Oops - embarrassing; my proof by counter-example shows that tabs are not equivalent to 4 spaces. As Alex Martelli points out in a comment, tabs are equivalent to 8 spaces, and adapting the example with a tab and 8 spaces shows that this is indeed the case.
x = 1
if x != 1:
^Iprint "x is not 1\n"
print "y is unset\n"
This code works, printing nothing.
Changed to Community Wiki since I don't deserve any (extra) credit.
Jonathan Leffler
2010-01-09 18:59:33
Unfortunately, tabs ARE considered equivalent to spaces -- specifically, eight spaces, as the docs say quite clearly. Never mixing tabs and spaces is best-practice, but you need to run Python with `-t` (or `-tt`) to get warnings (or errors) for violations of said best practice.
Alex Martelli
2010-01-09 19:12:42
+2
A:
Just don't interchange them :)
Set your IDE/editor to input 4 spaces upon pressing "tab" and you are good to go.
shylent
2010-01-09 19:01:18
+3
A:
I would recommend that you go through http://www.python.org/dev/peps/pep-0008/ which is the 'official' python style guide for Python code. It covers (among other things) the use of tabs/spaces.
Noufal Ibrahim
2010-01-09 19:01:45
+7
A:
Follow PEP 8 for Python style. PEP 8 says: Indentation
Use 4 spaces per indentation level.
For really old code that you don't want to mess up, you can continue to
use 8-space tabs.
Tabs or Spaces?
Never mix tabs and spaces.
The most popular way of indenting Python is with spaces only. The
second-most popular way is with tabs only. Code indented with a mixture
of tabs and spaces should be converted to using spaces exclusively. When
invoking the Python command line interpreter with the -t option, it issues
warnings about code that illegally mixes tabs and spaces. When using -tt
these warnings become errors. These options are highly recommended!
Eli Bendersky
2010-01-09 19:02:22
A:
I believe that the tab character should simply never appear in source code under any circumstances. There's no advantage to it and it's an endless source of tiny errors. - use a character string with \t if you need a tab, it has the advantage that it's self-documenting.
Here's the classic article about tabs vs spaces - I use a variant of jwz's elisp in my own .emacs file.
(I confess to personally breaking with PEP 8 by using only 2 characters' indentation - 4 characters is a lot when your lines are only 80 characters...)
Tom Swirly
2010-01-09 23:04:40