Inline Calculation of Dictionary Values

[++imanshu]

Hi,

Is it possible to something along these lines in python :-

map = {
'key1': f(),
'key2': modify_state(); val = f(); restore_state(); val,
'key3': f(),
}

For 'key2' I want to store the value returned by f() but after
modifying the state. Do we have something like a "bare block". I am
trying to avoid this :-

def f2():
modify_state()
val = f()
restore_state()
return val

map = {
'key1': f(),
'key2': f2()
'key3': f(),
}

Thank You,
Himanshu

[Chris Rebert]

On Wed, Apr 21, 2010 at 5:51 AM, ++imanshu <himans...@gmail.com> wrote:
>     Is it possible to something along these lines in python :-
>
> map = {
> 'key1': f(),
> 'key2': modify_state(); val = f(); restore_state(); val,
> 'key3': f(),
> }
>
>      For 'key2' I want to store the value returned by f() but after
> modifying the state. Do we have something like a "bare block".

Based on what I can find about "bare blocks", Nope. And we like it that way :-)

> I am
> trying to avoid this :-
>
> def f2():
>     modify_state()
>     val = f()
>     restore_state()
>     return val
>
> map = {
> 'key1': f(),
> 'key2': f2()
> 'key3': f(),
> }

FWIW, I don't see what's wrong with this. You could probably refactor
f2() to use the `with` statement and a context manager, but that's
getting tangential.
However, the question arises: Why do you have global state in the first place?

Cheers,
Chris
--
http://blog.rebertia.com

[Dave Angel]

How about something like:

mymap = {
'key1': f(),
'key2': [modify_state(), f(), restore_state()][1],
'key3': f(),
}

This builds a list of three values, and uses only the [1] item from the
list.

DaveA

[++imanshu]

This is cool. I'll use it.

Thank You,
Himanshu

[++imanshu]

On Apr 21, 6:10 pm, Chris Rebert <c...@rebertia.com> wrote:

f() = flavor independent os api for getting path to a folder, uses
effective user id (eg Folder.FSFindFolder(Folders.kUserDomain,
Folders.kInternetPlugInFolderType, Folders.kDontCreateFolder))
modify_state() = change current effective user id
restore_state() = restore to old user id

Thanks for the reply.

Thank You,
Himanshu

[Peter Otten]

Dave Angel wrote:

Please think of the children ;)

The function based approach is the way to go:

def f2():
cookie = modify_state()
try:
return f()
finally:
restore_state(cookie)

This will restore the state even if f() raises an exception.

If you want something more fancy you can parameterize f2() by the three
functions or look into context managers.

Peter