python - Why nested list indexing gets swapped with list comprehensions? -


i expected following 2 code-segments equivalent.

return tuple(tuple( false if (i,j) in neighborhood else avail[i][j]     in range(len(avail)))          j in range(len(avail[i])))  (false, false, true, true, true) (false, false, true, true, true) (false, false, true, true, true) (false, false, true, true, true) (true, true, true, true, true)  ls = [[val val in row] row in avail] in range(len(avail)):     j in range(len(avail[i])):         if (i,j) in neighborhood:             ls[i][j] = false return ls  [false, false, false, false, true] [false, false, false, false, true] [true, true, true, true, true] [true, true, true, true, true] [true, true, true, true, true]

the 1 for-loops "correct" (thats wanted). why did list comprehension-version swap indexes?

you have loops inverted in first version. creating inner tuples looping on range(len(avail)) , outer tuples loop on range(len(avail[i])).

your code equivalent (with lists instead of tuples) of instead:

outer = [] j in range(len(avail[i])):     inner = []     in range(len(avail)):         inner.append(false if (i,j) in neighborhood else avail[i][j])     outer.append(inner)

and relied on i still being assigned global. can see when indent expression based on parenthesis:

return tuple(     tuple(         false if (i,j) in neighborhood else avail[i][j]         in range(len(avail))     )          j in range(len(avail[i])) )

reverse loops (indented differently communicate grouping better):

return tuple(     tuple(false if (i,j) in neighborhood else avail[i][j] j in range(len(avail[i])))          in range(len(avail)))

the above equivalent of:

outer = [] in range(len(avail)):     inner = []     j in range(len(avail[i])):         inner.append(false if (i,j) in neighborhood else avail[i][j])     outer.append(inner)

you can simplify code using enumerate():

return tuple(     tuple(false if (i,j) in neighborhood else v j, v in enumerate(row))         i, row in enumerate(avail))

Comments

Post a Comment

Popular posts from this blog

image - ClassNotFoundException when add a prebuilt apk into system.img in android -

i'm in trouble add prebuilt apk system.img based taiwan mtk android phone platform, when push apk onto device,after reboot phone,the apk can installed succecessfully,but if add apk alps/out/target/product/$prj/system/app or vendor/mediatek/$prj/artifacts/out/target/product/$prj/system/app ,and produce system.img,the apk can't installed normally,the logcat say: a.lang.runtimeexception: unable instantiate activity componentinfo{com.sec.android.widgetapp.ap.hero.accuweather.widget/com.sec.android.widgetapp.ap.hero.accuweather.widget.weatherclock}: java.lang.classnotfoundexception: com.sec.android.widgetapp.ap.hero.accuweather.widget.weatherclock. can tell me what's problem ? when package manager installs apps part of system partition different installing apps on data partition. looks app using libraries somewhere else. when install on data lib directory created in apps data directory , symlinked /data/app-lib/. when apps installed on system it's expecte...
Read more

I need to import mysql 5.1 to 5.5? -

i have mysql 5.1 database , need import localhost running 5.5. how import 5.5 or downgrade mysql? install phpmyadmin 5.1 os: http://www.wikihow.com/install-phpmyadmin-on-your-windows-pc or https://www.digitalocean.com/community/articles/how-to-install-and-secure-phpmyadmin-on-ubuntu-12-04 then login, click on database, hit export, , export in sql format (quick fine). import .sql file 5.5 server (after installing phpmyadmin) logging in clicking database , hit import. hope helps!
Read more

Java, Hibernate, MySQL - store UTC date-time -

i saw here on few related questions (like this one , of course, this one )... essentially, want store date-time utc, , let application user choose time zone wants display date-time in. since seems date-time fields affected underlying jdbc driver, wonder if acceptable way go storing utc date-time: set both mysql , application server machine utc time zone (no need separate) both mysql , jvm should pick underlying system time settings (if not instructed otherwise) use datetime table columns on mysql side use java.util.date corresponding mapping on hibernate side (i guess java.sql.timestamp used too) let application worry interpreting date-time fields - i.e. let user choose preferred time zone is ok? edit clarify - here meant refer timestamps created strictly on server (e.g.date-time of record creation). application server instantiates date objects (new date() equals current date-time on server, , time zone agnostic). if client user wants supply date searching/filte...
Read more