PEP 8 is pretty much "the root" of all common style guides.
Google's Python style guide has some parts that are quite well thought of, but others are idiosyncratic (the two-space indents instead of the popular four-space ones, and the CamelCase style for functions and methods instead of the camel_case style, are pretty major idiosyncrasies).
On to your specific questions:
1.- What is the most widely used column width? (the eternal question) I'm currently sticking to 80 columns (and it's a pain!)
80 columns is most popular
2.- What quotes to use? (I've seen everything and PEP 8 does not mention anything clear) I'm using single quotes for everything but docstrings, which use triple double quotes.
I prefer the style you're using, but even Google was not able to reach a consensus about this:-(
3.- Where do I put my imports? I'm putting them at file header in this order.
import sys import -rest of python modules needed-
import whatever import -rest of application modules-
Yes, excellent choice, and popular too.
4.- Can I use "import whatever.function as blah"? I saw some documents that disregard doing this.
I strongly recommend you always import modules -- not specific names from inside a module. This is not just style -- there are strong advantages e.g. in testability in doing that. The as clause is fine, to shorten a module's name or avoid clashes.
5.- Tabs or spaces for indenting? Currently using 4 spaces tabs.
Overwhelmingly most popular.
6.- Variable naming style? I'm using lowercase for everything but classes, which I put in camelCase.
Almost everybody names classes with uppercase initial and constants with all-uppercase.
1.- Most everyone has a 16:9 or 16:10 monitor now days. Even if they don't have a wide-screen they have lots of pixels, 80 cols isn't a big practical deal breaker like it was when everyone was hacking at the command line in a remote terminal window on a 4:3 monitor at 320 X 240. I usually end the line when it gets too long, which is subjective. I am at 2048 X 1152 on a 23" Monitor X 2.
2.- Single quotes by default so you don't have to escape Double quotes, Double quotes when you need to embed single quotes, and Triple quotes for strings with embedded newlines.
3.- Put them at the top of the file, sometimes you put them in the main function if they aren't needed globally to the module.
4.- It is a common idiom to rename some modules. A good example is the following.
try:
# for Python 2.6.x
import json
except ImportError:
# for previous Pythons
try:
import simplejson as json
except ImportError:
sys.exit('easy_install simplejson')
but the preferred way to import just a class or function is from module import xxx with the optional as yyy if needed
5.- Always use SPACES! 2 or 4 as long as no TABS
6.- Classes should up UpperCaseCamelStyle, variables are lowercase sometimes lowerCamelCase or sometimes all_lowecase_separated_by_underscores, as are function names. "Constants" should be ALL_UPPER_CASE_SEPARATED_BY_UNDERSCORES
When in doubt refer to the PEP 8, the Python source, existing conventions in a code base. But the most import thing is to be internally consistent as possible. All Python code should look like it was written by the same person when ever possible.