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.

an example of a language feature that isn t just removing line breaks, although still not convinced this is clearer than the more verbose version

a = 1 if x > 15 else 2

for a in someList:
    list.append(splitColon.split(a))

You can rewrite the above as:

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

Python lets you put the indented clause on the same line if it s only one line:

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

def squared(x): return x * x

class MyException(Exception): pass

You could do all of that in one line by omitting the example variable:

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

Older versions of Python would only allow a single simple statement after for ...: if ...: or similar block introductory statements.

I see that one can have multiple simple statements on the same line as any of these. However, there are various combinations that don t work. For example we can:

for i in range(3): print "Here s i:"; print i

... but, on the other hand, we can t:

for i in range(3): if i % 2: print "That s odd!"

We can:

x=10
while x > 0: print x; x-=1

... but we can t:

x=10; while x > 0: print x; x-=1

... and so on.

In any event all of these are considered to be extremely NON-pythonic. If you write code like this then experience Pythonistas will probably take a dim view of your skills.

It s marginally acceptable to combine multiple statements on a line in some cases. For example:

x=0; y=1

... or even:

if some_condition(): break

... for simple break continue and even return statements or assigments.

In particular if one needs to use a series of elif one might use something like:

if     keystroke ==  q :   break
elif   keystroke ==  c :   action= continue 
elif   keystroke ==  d :   action= delete 
# ...
else:                      action= ask again 

... then you might not irk your colleagues too much. (However, chains of elif like that scream to be refactored into a dispatch table ... a dictionary that might look more like:

dispatch = {
     q : foo.break,
     c : foo.continue,
     d : foo.delete
    }


# ...
while True:
    key = SomeGetKey()
    dispatch.get(key, foo.try_again)()

Dive into python has a bit where he talks about what he calls the and-or trick, which seems like an effective way to cram complex logic into a single line.

Basically, it simulates the ternary operater in c, by giving you a way to test for truth and return a value based on that. For example:

>>> (1 and ["firstvalue"] or ["secondvalue"])[0]
"firstvalue"
>>> (0 and ["firstvalue"] or ["secondvalue"])[0]
"secondvalue"

This is an example of "if else" with actions.

>>> def fun(num):
    print  This is %d  % num
>>> fun(10) if 10 > 0 else fun(2)
this is 10
OR
>>> fun(10) if 10 < 0 else 1
1