This was my source I started with. My List L = [0, 23, 234, 89, None, 0, 35, 9] When I run this : L = filter(None, L) I get this results [23, 234, 89, 35, 9] But this is not what I need, what I really need is : [0, 23, 234, 89, 0, … Read more
In Python you can have multiple iterators in a list comprehension, like [(x,y) for x in a for y in b] for some suitable sequences a and b. I’m aware of the nested loop semantics of Python’s list comprehensions. My question is: Can one iterator in the comprehension refer to the other? In other words: … Read more
This question already has answers here: How to make a flat list out of a list of lists? (31 answers) Closed 5 years ago. Is there a simple way to flatten a list of iterables with a list comprehension, or failing that, what would you all consider to be the best way to flatten a … Read more
As we all know, there’s list comprehension, like [i for i in [1, 2, 3, 4]] and there is dictionary comprehension, like {i:j for i, j in {1: ‘a’, 2: ‘b’}.items()} but (i for i in (1, 2, 3)) will end up in a generator, not a tuple comprehension. Why is that? My guess is … Read more
Is it possible to create a dictionary comprehension in Python (for the keys)? Without list comprehensions, you can use something like this: l = [] for n in range(1, 11): l.append(n) We can shorten this to a list comprehension: l = [n for n in range(1, 11)]. However, say I want to set a dictionary’s … Read more
When should you use generator expressions and when should you use list comprehensions in Python? # Generator expression (x*2 for x in range(256)) # List comprehension [x*2 for x in range(256)] 12 s 12 John’s answer is good (that list comprehensions are better when you want to iterate over something multiple times). However, it’s also … Read more
index() will give the first occurrence of an item in a list. Is there a neat trick which returns all indices in a list for an element? 17 s 17 You can use a list comprehension with enumerate: indices = [i for i, x in enumerate(my_list) if x == “whatever”] The iterator enumerate(my_list) yields pairs … Read more
This question already has answers here: if/else in a list comprehension (12 answers) Closed 5 years ago. I have a list l: l = [22, 13, 45, 50, 98, 69, 43, 44, 1] For numbers above 45 inclusive, I would like to add 1; and for numbers less than it, 5. I tried [x+1 for … Read more
I want to create a series of lists, all of varying lengths. Each list will contain the same element e, repeated n times (where n = length of the list). How do I create the lists, without using a list comprehension [e for number in xrange(n)] for each list? 8 s 8 You can also … Read more
Is there a reason to prefer using map() over list comprehension or vice versa? Is either of them generally more efficient or considered generally more pythonic than the other? 14 s 14 map may be microscopically faster in some cases (when you’re NOT making a lambda for the purpose, but using the same function in … Read more
