Are one-line 'if'/'for'-statements good Python style?

Well,

if "exam" in "example": print "yes!"

Is this an improvement? No. You could even add more statements to the body of the if-clause by separating them with a semicolon. I recommend against that though.

I've found that in the majority of cases doing block clauses on one line is a bad idea.

It will, again as a generality, reduce the quality of the form of the code. High quality code form is a key language feature for python.

In some cases python will offer ways todo things on one line that are definitely more pythonic. Things such as what Nick D mentioned with the list comprehension:

newlist = [splitColon.split(a) for a in someList]

although unless you need a reusable list specifically you may want to consider using a generator instead

listgen = (splitColon.split(a) for a in someList)

note the biggest difference between the two is that you can't reiterate over a generator, but it is more efficient to use.

There is also a built in ternary operator in modern versions of python that allow you to do things like

string_to_print = "yes!" if "exam" in "example" else ""print string_to_print

or

iterator = max_value if iterator > max_value else iterator

Some people may find these more readable and usable than the similar if (condition): block.

When it comes down to it, it's about code style and what's the standard with the team you're working on. That's the most important, but in general, i'd advise against one line blocks as the form of the code in python is so very important.

More generally, all of the following are valid syntactically:

if condition:    do_something()if condition: do_something()if condition:    do_something()    do_something_else()if condition: do_something(); do_something_else()

...etc.