idioms

I feel like almost every time I read a file in Python, what I want is: with open("filename") as file_handle: for line in file_handle: #do something Is this truly the preferred idiom? It mildly irritates me that this double indents all file reading logic. Is there a way to collapse this logic into one line or one layer? For simple cases, yes, the two-level with and for is idiomatic. For cases where the indentation becomes a problem, here as anywhere else in Python, the idiomatic solution is to find something to factor out into a function. You can write wrappers to help this. For example, here's

I'm just wondering, is there a Python idiom to check if a string is empty, and then print a default if it's is? (The context is Django, for the __unicode__(self) function for UserProfile - basically, I want to print the first name and last name, if it exists, and then the username if they don't both exist). Cheers, Victor displayname = firstname + lastname or username will work if firstname and last name has 0 length blank string displayname = firstname+' '+lastname if firstname and lastname else username I think this issue is better handled in the templates with something like: {{ user.get

This question already has an answer here: In ArrayBlockingQueue, why copy final member field into local final variable? 2 answers While browsing through the source code of the java.util.concurrency package, I noticed an idiomatic use of ReentrantLock that I had not seen before: member RentrantLock variables were never accessed directly from within a method - they were always referenced by a local variable reference. Style #1 e.g from java.util.concurrent.ThreadPoolExecutor private final ReentrantLock mainLock = new ReentrantLock(); ... // why a local reference to final mainlock instead of

I'm looking for a clean, Pythonic, way to eliminate from the following list: li = [0, 1, 2, 3, 3, 4, 3, 2, 2, 2, 1, 0, 0] all contiguous repeated elements (runs longer than one number) so as to obtain: re = [0, 1, 2, 4, 3, 1] but although I have working code, it feels un-Pythonic and I am quite sure there must be a way out there (maybe some lesser known itertools functions?) to achieve what I want in a far more concise and elegant way. Here is a version based on Karl's which doesn't requires copies of the list ( tmp , the slices, and the zipped list). izip is significantly faster than (Python

I am computing a dplyr::summarize across a dataframe of sales data. I do a group-by (S,D,Y), then within each group, compute medians and means for weeks 5..43, then merge those back into the parent df. Variable X is sales. X is never NA (i.e. there are no explicit NAs anywhere in df), but if there is no data (as in, no sales) for that S,D,Y and set of weeks, there will simply be no row with those values in df (take it that means zero sales for that particular set of parameters). In other words, impute X=0 in any structurally missing rows (but I hope I don't need to melt/cast the original df,

I just saw this nice copy-on-write pointer implementation. It looks pretty generic and useful, so my question is: Is such a class contained in any of the C++ toolkits (boost, loki, etc.)? If not, I'd really like to know why because it is a really useful idiom and apparently a generic implementation seems doable (like the one I linked to). There was a lot of debate over the possibility, and at least one suggested version of what eventually came out as auto_ptr was for a reference counted COW pointer. Unfortunately, the time for COW has mostly passed. Making a COW pointer (or COW-whatever)

When taking a substring of a string in Go, no new memory is allocated. Instead, the underlying representation of the substring contains a Data pointer that is an offset of the original string's Data pointer. This means that if I have a large string and wish to keep track of a small substring, the garbage collector will be unable to free any of the large string until I release all references to the shorter substring. Slices have a similar problem, but you can get around it by making a copy of the subslice using copy(). I am unaware of any similar copy operation for strings. What is the