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• why the hell does x,y = zip(*zip(a,b)) work in Python?

  - by Mike Dewar

  OK I love Python's zip() function. Use it all the time, it's brilliant. Every now and again I want to do the opposite of zip(), think "I used to know how to do that", then google python unzip, then remember that one uses this magical * to unzip a zipped list of tuples. Like this: x = [1,2,3] y = [4,5,6] zipped = zip(x,y) unzipped_x, unzipped_y = zip(*zipped) unzipped_x Out[30]: (1, 2, 3) unzipped_y Out[31]: (4, 5, 6) What on earth is going on? What is that magical asterisk doing? Where else can it be applied and what other amazing awesome things in Python are so mysterious and hard to google?

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• Using Python's ConfigParser to read a file without section name

  - by Arrieta

  Hello: I am using ConfigParser to read the runtime configuration of a script. I would like to have the flexibility of not providing a section name (there are scripts which are simple enough; they don't need a 'section'). ConfigParser will throw the NoSectionError exception, and will not accept the file. How can I make ConfigParser simply retrieve the (key, value) tuples of a config file without section names? For instance: key1=val1 key2:val2 I would rather not write to the config file.

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• Would this hack for per-object permissions in django work?

  - by Edward

  According to the documentation, a class can have the meta option permissions, described as such: Options.permissions Extra permissions to enter into the permissions table when creating this object. Add, delete and change permissions are automatically created for each object that has admin set. This example specifies an extra permission, can_deliver_pizzas: permissions = (("can_deliver_pizzas", "Can deliver pizzas"),) This is a list or tuple of 2-tuples in the format (permission_code, human_readable_permission_name). Would it be possible to define permissions at run time by: permissions = (("can_access_%s" % self.pk, / "Has access to object %s of type %s" % (self.pk,self.__name__)),) ?

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• Python: needs more than 1 value to unpack

  - by Rosarch

  What am I doing wrong to get this error? replacements = {} replacements["**"] = ("<strong>", "</strong>") replacements["__"] = ("<em>", "</em>") replacements["--"] = ("<blink>", "</blink>") replacements["=="] = ("<marquee>", "</marquee>") replacements["@@"] = ("<code>", "</code>") for delimiter, (open_tag, close_tag) in replacements: # error here message = self.replaceFormatting(delimiter, message, open_tag, close_tag); The error: Traceback (most recent call last): File "", line 1, in for shit, (a, b) in replacements: ValueError: need more than 1 value to unpack All the values tuples have two values. Right?

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• Sort and Group in LINQ

  - by Jono

  I apologise in advance if this has been answered before; it seems so fundamental to me yet I haven't turned up the answer in any of my searches. I have a list of string tuples, say (P1,P2) I'd like to know if there's a LINQ statement where I could group by P1 (in ascending order), and have that group contain all the P2 values for the group (in descending order). For input: ("A","B"), ("A","C"), ("D","B") I'd like to get two groups: "A" and "D" (in that order, every time) where group "A" contains "C" and "B" (in that order, every time) and group "D" contains, well, "B". Is this possible with the built-in LINQ classes or do I need to iterate the groups and sort them myself? Sounds like hard work~

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• Best data-structure to use for two ended sorted list

  - by fmark

  I need a collection data-structure that can do the following: Be sorted Allow me to quickly pop values off the front and back of the list Remain sorted after I insert a new value Allow a user-specified comparison function, as I will be storing tuples and want to sort on a particular value Thread-safety is not required Optionally allow efficient haskey() lookups (I'm happy to maintain a separate hash-table for this though) My thoughts at this stage are that I need a priority queue and a hash table, although I don't know if I can quickly pop values off both ends of a priority queue. I'm interested in performance for a moderate number of items (I would estimate less than 200,000). Another possibility is simply maintaining an OrderedDictionary and doing an insertion sort it every-time I add more data to it. Furthermore, are there any particular implementations in Python. I would really like to avoid writing this code myself.

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• top-k selection/merge

  - by tcurdt

  I have n sorted lists. These lists are quite long (300000+ tuples). Selecting the top 10 of the individual lists is of course trivial - they are right at the head of the lists. Where it gets more interesting is when I want the top 10 of all the sorted lists. The question is whether there is an algorithm to calculate the combined top 10 having the correct order while cutting off the long tail of the lists. The goal is to reduce the required space. And if there is: How does one find the limit where is is safe to cut? Note: The actual counts are not important. Only the order is.

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• calling a function from another function in python

  - by user1040503

  I have written this function that takes to strings in order to see if they are anagrams: def anagram_check(str_x, str_y): x = string1.replace(" ","") y = string2.replace(" ","") lower1 = x.lower() lower2 = y.lower() sorted1 = sorted(lower1) sorted2 = sorted(lower2) if sorted1 == sorted2: return True else: return False this function works fine, the problem is that now I need to use this function in another function in order to find anagrams in a text file. I want to print a list of tuples with all the anagrams in it. this is what i have done so far def anagrams_finder(words_num): anagrams = [] f = open("words.txt") a = list(f) list1 = ([s.replace('\n', '') for s in a]) list2 = ([i.lower() for i in list1]) list3 = list2[0:words_num] #number of words from text that need to be checked. for i in list3: .... I tried using for loops, while loops, appand.... but nothing seems to work. how can I use the first function in order to help me with the second? Please help...

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• Storm Trident 'average aggregator

  - by E Shindler

  I am a newbie to Trident and I'm looking to create an 'Average' aggregator similar to 'Sum(), but for 'Average'.The following does not work: public class Average implements CombinerAggregator<Long>.......{ public Long init(TridentTuple tuple) { (Long)tuple.getValue(0); } public Long Combine(long val1,long val2){ return val1+val2/2; } public Long zero(){ return 0L; } } It may not be exactly syntactically correct, but that's the idea. Please help if you can. Given 2 tuples with values [2,4,1] and [2,2,5] and fields 'a','b' and 'c' and doing an average on field 'b' should return '3'. I'm not entirely sure how init() and zero() work. Thank you so much for your help in advance. Eli

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• Using list comprehension in Python to do something similar to zip()?

  - by jamieb

  I'm a Python newbie and one of the things I am trying to do is wrap my head around list comprehension. I can see that it's a pretty powerful feature that's worth learning. cities = ['Chicago', 'Detroit', 'Atlanta'] airports = ['ORD', 'DTW', 'ATL'] print zip(cities,airports) [('Chicago', 'ORD'), ('Detroit', 'DTW'), ('Atlanta', 'ATL')] How do I use list comprehension so I can get the results as a series of lists within a list, rather than a series of tuples within a list? [['Chicago', 'ORD'], ['Detroit', 'DTW'], ['Atlanta', 'ATL']] (I realize that dictionaries would probably be more appropriate in this situation, but I'm just trying to understand lists a bit better). Thanks!

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• How to sort a list by the 2nd tuple element in python and C#

  - by user350468

  I had a list of tuples where every tuple consists of two integers and I wanted to sort by the 2nd integer. After looking in the python help I got this: sorted(myList, key=lambda x: x[1]) which is great. My question is, is there an equally succinct way of doing this in C# (the language I have to work in)? I know the obvious answer involving creating classes and specifying an anonymous delegate for the whole compare step but perhaps there is a linq oriented way as well. Thanks in advance for any suggestions.

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• Sorting by key > 10 integer sequences. with thrust

  - by smilingbuddha

  I want to perform a sort_by_key where I have a single key-sequence and multiple value sequences. One usually performs this with sort_by_key( key, key + N, make_zip_iterator( make_tuple(x1 , x2 , ...) ) ) However I want to perform a sort with 10 sequences each of length N. Thrust does not support tuples of size = 10. So is there a way around this ? Of course one can keep a separate copy of the key vector and perform sorts on bunches of 10 sequences. But I would like to do everything in a single call.

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• Python and database

  - by axl456

  hello.. Am working on a personal project, where i need to manipulate values in a database-like format.. Up until now, am using dictionaries, tuples, and list to store and consult those values. Am thinking about starting to use SQL to manipulate those values, but I dont know if its worth the effort, because I dont know anything about SQL, and I dont want to use something that wont bring me any benefits (if I can do it in a simpler way, i dont want to complicate things) if am only storing and consulting values, what would be the benefit of using SQL? PS: the numbers of row goes between 3 and 100 and the number of columns is around 10 (some may have 5 some may have 10 etc)

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• What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

  - by Seun Osewa

  I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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• Retrieving values from Env in mod_esi or webtools

  - by williamstw

  A complete noob question, but how exactly do I get values (e.g. path_info) from inside the callback? From the docs, I thought it was a list of tuples, which I thought would make it accessible via lists:keyfind, but I've had no luck. So far, all the examples I've found only show how to print everything with io_lib but not how to access the values by key... Thanks, --tim The docs: Module:Function(SessionID, Env, Input)- _ Types SessionID = term() Env = [EnvironmentDirectives] ++ ParsedHeader EnvironmentDirectives = {Key, Value} Key = query_string | content_length | server_software | gateway_interface | server_protocol | server_port | request_method | remote_addr | script_name. <v>Input = string()

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• Mapping over multiple Seq in Scala

  - by bsdfish

  Suppose I have val foo : Seq[Double] = ... val bar : Seq[Double] = ... and I wish to produce a seq where the baz(i) = foo(i) + bar(i). One way I can think of to do this is val baz : Seq[Double] = (foo.toList zip bar.toList) map ((f: Double, b : Double) => f+b) However, this feels both ugly and inefficient -- I have to convert both seqs to lists (which explodes with lazy lists), create this temporary list of tuples, only to map over it and let it be GCed. Maybe streams solve the lazy problem, but in any case, this feels like unnecessarily ugly. In lisp, the map function would map over multiple sequences. I would write (mapcar (lambda (f b) (+ f b)) foo bar) And no temporary lists would get created anywhere. Is there a map-over-multiple-lists function in Scala, or is zip combined with destructuring really the 'right' way to do this?

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• infix formula in the input

  - by gcc

  input: sqrt(2 - sin(3*A/B)^2.5) + 0.5*(C*~(D) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input : sqrt(2 - asin(3*A/B)^2.5) +cos(0.5*(C*~(D)) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input: sqrt(2 - sin(3*A/B)^2.5)/(0.5*(C*~(D)) + sin(3.11) +ln(B)) /*max lenght of formula is 250 characters*/ a b /*there are values for a,b,c,d */ c /*each variable with set of floating numbers*/ d As you can see infix formula in the input depends on user. My program will take a formula and n-tuples value. Then it calculate the results for each value of a,b,c and d. If you wonder I am saying ;outcome of program is graph. I dont know way how to store the formula so that I can do my job with easy. can you show me? a,b,c,d is letters cos,sin,sqrt,ln is function

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• Partially flattening a list

  - by alj

  This is probably a really silly question but, given the example code at the bottom, how would I get a single list that retain the tuples? (I've looked at the itertools but it flattens everything) What I currently get is: ('id', 20, 'integer') ('companyname', 50, 'text') [('focus', 30, 'text'), ('fiesta', 30, 'text'), ('mondeo', 30, 'text'), ('puma', 30, 'text')] ('contact', 50, 'text') ('email', 50, 'text') what I would like is a single level list like: ('id', 20, 'integer') ('companyname', 50, 'text') ('focus', 30, 'text') ('fiesta', 30, 'text') ('mondeo', 30, 'text') ('puma', 30, 'text') ('contact', 50, 'text') ('email', 50, 'text') def getproducts(): temp_list=[] product_list=['focus','fiesta','mondeo','puma'] #usually this would come from a db for p in product_list: temp_list.append((p,30,'text')) return temp_list def createlist(): column_title_list = ( ("id",20,"integer"), ("companyname",50,"text"), getproducts(), ("contact",50,"text"), ("email",50,"text"), ) return column_title_list for item in createlist(): print item Thanks ALJ

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• Finding a Eulerian Tour

  - by user590903

  I am trying to solve a problem on Udacity described as follows: # Find Eulerian Tour # # Write a function that takes in a graph # represented as a list of tuples # and return a list of nodes that # you would follow on an Eulerian Tour # # For example, if the input graph was # [(1, 2), (2, 3), (3, 1)] # A possible Eulerian tour would be [1, 2, 3, 1] I came up with the following solution, which, while not as elegant as some of the recursive algorithms, does seem to work within my test case. def find_eulerian_tour(graph): tour = [] start_vertex = graph[0][0] tour.append(start_vertex) while len(graph) > 0: current_vertex = tour[len(tour) - 1] for edge in graph: if current_vertex in edge: if edge[0] == current_vertex: current_vertex = edge[1] else: current_vertex = edge[0] graph.remove(edge) tour.append(current_vertex) break return tour graph = [(1, 2), (2, 3), (3, 1)] print find_eulerian_tour(graph) >> [1, 2, 3, 1] However, when submitting this, I get rejected by the grader. I am doing something wrong? I can't see any errors.

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• Iterating over a database column in Django

  - by curious

  I would like to iterate a calculation over a column of values in a MySQL database. I wondered if Django had any built-in functionality for doing this. Previously, I have just used the following to store each column as a list of tuples with the name table_column: import MySQLdb import sys try: conn = MySQLdb.connect (host = "localhost", user = "user", passwd="passwd", db="db") except MySQLdb.Error, e: print "Error %d: %s" % (e.args[0], e.args[1]) sys.exit (1) cursor = conn.cursor() for table in ['foo', 'bar']: for column in ['foobar1', 'foobar2']: cursor.execute('select %s from %s' % (column, table)) exec "%s_%s = cursor.fetchall()" % (table, column) cursor.close() conn.commit() conn.close() Is there any functionality built into Django to more conveniently iterate through the values of a column in a database table? I'm dealing with millions of rows so speed of execution is important.

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• Show parts of the result of an SQL statement using PHP

  - by mouthpiec

  I have an SQL query which returns a set of data (around 40-50 tuples). I would like to display the results 5 at a time on an HTML page using PHP. I already managed to have the right SELECT statement, but i am having problems to display the results 5 by 5 using a "more" button. Can you please help? Note that every time i call the query, the data is being randomized, so it is not possible to set limits and call the query again. I have to find the method to store the results somewhere, and then show them 5 by 5.

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• SQL finding overlapping of times pass midnight (across 2 days)

  - by janechii

  Hi everyone, I know there are lots of these types of questions, but i didn't see one that was similar enough to my criteria. So i'd like to ask for your help please. The fields i have are just start and end which are of time types. I cannot involve any specific dates in this. If the time ranges don't go pass midnight across day, i'd just compare two tuples as such: end1 > start2 AND start1 < end2 (end points touching are not considered overlapped here.) But when I involve time range that pass (or at) midnight, this obviously doesn't work. For example, given: start | end --------+-------- 06:00PM | 01:00AM 03:00PM | 09:00PM Without involving dates, how can i achieve this, please. My assumption is, if end is less than start, then we're involving 2 days. I'm trying to do this in plain standard SQL, so just a simple and concise logic in the WHERE clause. Thank you everyone!

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• Bash intercepting wildcard in script

  - by MrRoth

  I am using Bash script to read line by line from a text file, which has special characters in it (regular expression). When I use echo "${SOME_VAR}" it does not display the text as is. I am familiar with Prevent * to be expanded in the bash script. How can I display and use the text as is? UPDATE The text (TSV) file holds tuples similar to (the last entry is a psql query) bathroom bathroom select name from photos where name ~* '\mbathroom((s)?|(''s)?)\M'; I am reading the CSV as follows: tail -n+2 text.file | while IFS=$'\t' read x y z do echo "${z}" done which gives the output select name from photos where name ~* 'mbathroom((s)?|(''s)?)M'); note that the '\' is missing

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• F# working with while loop

  - by mamu

  I have a datareader and i want to return collection of rows from it, after reading books for like a day i am not able to find out best way to do it in f#. I can do it normal C# way in F# but that is not why i am using f# Here is what i am trying to achieve let values = while reader.Read() do yield reader.GetString(0), reader.GetInt64(1) Above is how i am trying to do all values get collected into values, which could be dictinary or tuples or any collection yield can't be used in while loop but that is what i am trying to do What could be the best way to achieve this

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• What do I do with a Concrete Syntax Tree?

  - by Cap

  I'm using pyPEG to create a parse tree for a simple grammar. The tree is represented using lists and tuples. Here's an example: [('command', [('directives', [('directive', [('name', 'retrieve')]), ('directive', [('name', 'commit')])]), ('filename', [('name', 'f30502')])])] My question is what do I do with it at this point? I know a lot depends on what I am trying to do, but I haven't been able to find much about consuming/using parse trees, only creating them. Does anyone have any pointers to references I might use? Thanks for your help.

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