No flaming please, asking as a community wiki so nobody gets reputation here. I know python is not the first language to have list comprehension. I'm just interest in the history of the name. I'm particularly interested in why it's called comprehension ...
EDIT: Clarified the question a bit How can I get a string from a dictionary with the format key1 = value1 key2 = value2 in a relatively fast way ? (relative to plain concatenation) ...
What is a way to implement similar functionality in Haskell of List comprehensions with guards in F# for example: factors :: Int -> [Int] factors = [x | x <-[1 .. n], n 'mod' x == 0] factors 15 [1,3,5,15] and posInt :: Int -> [Int] posInt = [n | n > 0] posInt 5 [5] posInt 0 [] ...
I'm a python newb and am having trouble groking nested list comprehensions. I'm trying to write some code to read in a file and construct a list for each character for each line. so if the file contains xxxcd cdcdjkhjasld asdasdxasda The resulting list would be: [ ['x','x','x','c','d'] ['c','d','c','d','j','k','h','j','a','s','l',...
I probably didn't ask correctly: I would like a list value that can match any list: the "inverse" of (None,) but even with (None,) it will match item as None (which I don't want) The point is I have a function working with: [x for x in my_list if x[field] not in filter_list] and I would like to filter everything or nothing without maki...
I got bored during the holiday season this year and randomly decided to write a simple list comprehension/filtering library for Java (I know there are some great ones out there, I just wanted to write it my self for the hell of it). For this list: LinkedList<Person> list = new LinkedList<Person>(); list.add(new Person("Jac...
Hi, I'm a Matlab user needing to use Python for some things, I would really appreciate it if someone can help me out with Python syntax: (1) Is it true that lists can be indexed by tuples in Python? If so, how do I do this? For example, I would like to use that to represent a matrix of data. (2) Assuming I can use a list indexed by t...
If have a list of dictionary items like so: L = [{"a":1, "b":0}, {"a":3, "b":1}...] I would like to split these entries based upon the value of "b", either 0 or 1. A(b=0) = [{"a":1, "b":1}, ....] B(b=1) = [{"a":3, "b":2}, .....] I am comfortable with using simple list comprehensions, and i am currently looping through the list L t...
Why is print(x) here not valid (SyntaxError) in the following list-comprehension? my_list=[1,2,3] [print(my_item) for my_item in my_list] To contrast - the following doesn't give a syntax error: def my_func(x): print(x) [my_func(my_item) for my_item in my_list] ...
I was trying to find the quickest way to count the number of items in a list matching a specific filter. In this case, finding how many odd numbers there are in a list. While doing this, I was surprised by the results of comparing a list comprehension vs the equivalent generator expression: python -m timeit -s "L = xrange(1000000)" "su...
Using Python, I'm trying to convert a sentence of words into a flat list of all distinct letters in that sentence. Here's my current code: words = 'She sells seashells by the seashore' ltr = [] # Convert the string that is "words" to a list of its component words word_list = [x.strip().lower() for x in words.split(' ')] # Now conver...
I have a nested dictionary of people and item ratings, with people as the key. people may or may not share items. Example: { 'Bob' : {'item1':3, 'item2':8, 'item3':6}, 'Jim' : {'item1':6, 'item4':7}, 'Amy' : {'item1':6,'item2':5,'item3':9,'item4':2} } I'm looking for the simplest way to flip these relations, and have a new nested d...
I've started working on some Project Euler problems, and have solved number 4 with a simple brute force solution: def mprods(a,b): c = range(a,b) f = [] for d in c: for e in c: f.append(d*e) return f max([z for z in mprods(100,1000) if str(z)==(''.join([str(z)[-i] for i in range(1,len(str(z))+1)]))]) After solving, I tried t...
I am curious if it is possible to dynamically build a list comprehension in Haskell. As an example, if I have the following: all_pows (a,a') (b,b') = [ a^y * b^z | y <- take a' [0..], z <- take b' [0..] ] I get what I am after *Main> List.sort $ all_pows (2,3) (5,3) [1,2,4,5,10,20,25,50,100] However, what I'd really like is to ha...
I'm trying to build a small testing app with erlang+mnesia. I have a user table build from the #user record, as defined here: -record(user_details, {name, password}). -record(user, {id, details}). then I insert a user with that function: add_sample_data() -> Mat = #user{ details = #user_details{ name = "mat", password ...
I have a list of users in local store that I need to update from a remote list of users every once in a while. Basically: If a remote user already exists locally, update its fields. If a remote user doesn't already exist locally, add the user. If a local user doesn't appear in the remote list, deactivate or delete. If a local user also...
I have a function to pick out lumps from a list of strings and return them as another list: def filterPick(lines,regex): result = [] for l in lines: match = re.search(regex,l) if match: result += [match.group(1)] return result Is there a way to reformulate this as a list comprehension? Obviously...
I need to generate a set of coordinates in Erlang. Given one coordinate, say (x,y) I need to generate (x-1, y-1), (x-1, y), (x-1, y+1), (x, y-1), (x, y+1), (x+1, y-1), (x+1, y), (x+1, y+1). Basically all surrounding coordinates EXCEPT the middle coordinate (x,y). To generate all the nine coordinates, I do this currently: [{X,Y} || X<-li...
Say I have a function func(i) that creates an object for an integer i, and N is some nonnegative integer. Then what's the fastest way to create a list (not a range) equal to this list mylist = [func(i) for i in range(N)] without resorting to advanced methods like creating a function in C? My main concern with the above list comprehens...
I have a generator (numbers) and a value (number). I would like to iterate over these as if they were one sequence: i for i in tuple(my_generator) + (my_value,) The problem is, as far as I undestand, this creates 3 tuples only to immediately discard them and also copies items in "my_generator" once. Better approch would be: def con(...