All Questions
Tagged with list python-2.7
2,997
questions
188
votes
9
answers
571k
views
Zip lists in Python
I am trying to learn how to "zip" lists. To this end, I have a program, where at a particular point, I do the following:
x1, x2, x3 = stuff.calculations(withdataa)
This gives me three lists, x1, x2, ...
- 5,725
179
votes
6
answers
363k
views
Insert an element at a specific index in a list and return the updated list
I have this:
>>> a = [1, 2, 4]
>>> print a
[1, 2, 4]
>>> print a.insert(2, 3)
None
>>> print a
[1, 2, 3, 4]
>>> b = a.insert(3, 6)
>>> print b
...
- 35.4k
134
votes
4
answers
244k
views
python filter list of dictionaries based on key value
I have a list of dictionaries and each dictionary has a key of (let's say) 'type' which can have values of 'type1', 'type2', etc. My goal is to filter out these dictionaries into a list of the same ...
- 1,603
128
votes
4
answers
29k
views
Why do tuples take less space in memory than lists?
A tuple takes less memory space in Python:
>>> a = (1,2,3)
>>> a.__sizeof__()
48
whereas lists takes more memory space:
>>> b = [1,2,3]
>>> b.__sizeof__()
64
...
- 1,698
119
votes
7
answers
214k
views
The most efficient way to remove first N elements in a list?
I need to remove the first n elements from a list of objects in Python 2.7. Is there an easy way, without using loops?
- 1,783
108
votes
2
answers
174k
views
How to get everything from the list except the first element using list slicing [duplicate]
So I have something that I am parsing, however here is an example of what I would like to do:
list = ['A', 'B', 'C']
And using list slicing have it return to me everything but the first index. So in ...
- 1,891
99
votes
10
answers
401k
views
Find empty or NaN entry in Pandas Dataframe
I am trying to search through a Pandas Dataframe to find where it has a missing entry or a NaN entry.
Here is a dataframe that I am working with:
cl_id a c d e ...
- 12.1k
98
votes
8
answers
150k
views
How to join entries in a set into one string?
Basically, I am trying to join together the entries in a set in order to output one string. I am trying to use syntax similar to the join function for lists. Here is my attempt:
list = ["gathi-109","...
- 21.8k
92
votes
2
answers
53k
views
Why is a list comprehension so much faster than appending to a list?
I was wondering why list comprehension is so much faster than appending to a list. I thought the difference is just expressive, but it's not.
>>> import timeit
>>> timeit.timeit(...
- 58.6k
75
votes
5
answers
174k
views
Remove list from list in Python [duplicate]
Possible Duplicate:
Get difference from two lists in Python
What is a simplified way of doing this? I have been trying on my own, and I can't figure it out.
list a and list b, the new list should ...
- 771
62
votes
7
answers
86k
views
How to check if key exists in list of dicts in python?
Say I have a list of dicts that looks like this:
[{1: "a"}, {2: "b"}]
What is the pythonic way to indicate if a certain key is in one of the dicts in the list?
- 789
61
votes
9
answers
198k
views
Converting string to tuple without splitting characters
I am striving to convert a string to a tuple without splitting the characters of the string in the process. Can somebody suggest an easy method to do this. Need a one liner.
Fails
a = 'Quattro ...
- 3,576
58
votes
3
answers
73k
views
List comprehension list of lists
I have a list of lists, and would like to use list comprehension to apply a function to each element in the list of lists, but when I do this, I end up with one long list rather than my list of lists.
...
- 3,573
55
votes
8
answers
122k
views
Getting a sublist of a Python list, with the given indices?
I have a Python list, say a = [0,1,2,3,4,5,6]. I also have a list of indices, say b = [0,2,4,5]. How can I get the list of elements of a with indices in b?
- 19.7k
54
votes
6
answers
31k
views
List unhashable, but tuple hashable?
In How to hash lists? I was told that I should convert to a tuple first, e.g. [1,2,3,4,5] to (1,2,3,4,5).
So the first cannot be hashed, but the second can. Why*?
*I am not really looking for a ...
- 72.7k
51
votes
2
answers
68k
views
Return a variable in a Python list with double quotes instead of single
I am trying to return a variable from a list of strings in double quotes rather than single.
For example, if my list is
List = ["A", "B"]
if I type List[0] the output is 'A'. Rather, I want "A". ...
- 3,172
45
votes
3
answers
131k
views
Write and read a list from file
This is a slightly weird request but I am looking for a way to write a list to file and then read it back some other time.
I have no way to remake the lists so that they are correctly formed/...
- 5,671
40
votes
4
answers
227k
views
TypeError: unsupported operand type(s) for -: 'list' and 'list'
I am trying to implement the Naive Gauss and getting the unsupported operand type error on execution.
Output:
execfile(filename, namespace)
File "/media/zax/MYLINUXLIVE/A0N-.py", line 26, in <...
- 537
40
votes
5
answers
32k
views
Sort a list with a custom order in Python
I have a list
mylist = [['123', 'BOOL', '234'], ['345', 'INT', '456'], ['567', 'DINT', '678']]
I want to sort it with the order of 1. DINT 2. INT 3. BOOL
Result:
[['567', 'DINT', '678'], ['345', '...
- 1,237
39
votes
2
answers
39k
views
How to sort list of lists according to length of sublists [duplicate]
I have the following list
a = [['a', 'b', 'c'], ['d', 'e'], ['f', 'g', 'h'], ['i', 'j', 'k', 'l'], ['m', 'n'], ['o']]
I would like to sort the list based on the length of their sub lists.
The ...
- 584
37
votes
4
answers
150k
views
How to check if a specific integer is in a list
I want to know how to make an if statement that executes a clause if a certain integer is in a list.
All the other answers I've seen ask for a specific condition like prime numbers, duplicates, etc. ...
- 421
35
votes
2
answers
18k
views
Efficiently filtering out 'None' items in a list comprehension in which a function is called
I have a list comprehension that calls a function which potentially returns None.
f = lambda x: x if x < 3 else None
l = [f(x) for x in [1,2,3,4]] # [1, 2, None, None]
I'd like to have the list ...
- 359
35
votes
3
answers
42k
views
sum each value in a list of tuples
I have a list of tuples similar to this:
l = [(1, 2), (3, 4), (5, 6), (7, 8), (9, 0)]
I want to create a simple one-liner that will give me the following result:
r = (25, 20) or r = [25, 20] # don'...
- 42.6k
35
votes
3
answers
46k
views
How to have a set of sets in Python? [duplicate]
In Python there's no full support for heterogeneous data structures. For example this fails:
set(set(1,2),set(2,3))
What's the best way to treat sets of sets?
user2760103
30
votes
3
answers
101k
views
Check if a key exists in a Python list
Suppose I have a list that can have either one or two elements:
mylist=["important", "comment"]
or
mylist=["important"]
Then I want to have a variable to work as a flag depending on this 2nd value ...
- 282k
29
votes
7
answers
29k
views
finding duplicates in a list of lists
I am using Python 2.7 and am trying to de-duplicate a list of lists and merge the values of the duplicates.
Right now I have:
original_list = [['a', 1], ['b', 1], ['a', 1], ['b', 1], ['b', 2], ['c', ...
- 8,625
28
votes
6
answers
31k
views
What is the difference between list and iterator in Python? [closed]
I am reading the book Think Python: How to think like a computer scientist, which says that in Python 3.x, dict([list of tuples]) returns an iterator instead of a list (as is the case in Python 2.7).
...
- 1,994
27
votes
1
answer
66k
views
Python iterate over two lists simultaneously [duplicate]
Is there a way in python to forloop over two or more lists simultaneously?
Something like
a = [1,2,3]
b = [4,5,6]
for x,y in a,b:
print x,y
to output
1 4
2 5
3 6
I know that I can do it with ...
- 1,134
27
votes
4
answers
16k
views
How does the min/max function on a nested list work?
Lets say, there is a nested list, like:
my_list = [[1, 2, 21], [1, 3], [1, 2]]
When the function min() is called on this:
min(my_list)
The output received is
[1, 2]
Why and How does it work? ...
- 10.9k
26
votes
9
answers
97k
views
Get max value from a list with lists?
So I have a list that contains several list which all have three strings first, then one float number, like:
resultlist = [["1", "1", "a", 8.3931], ["1", "2", "b", 6.3231], ["2", "1", "c", 9.1931]]
...
- 275
25
votes
2
answers
56k
views
XOR on two lists in Python [duplicate]
I'm a beginner in Python, and I have to do the XOR between two lists (the first one with the length : 600 and the other 60)
I really don't know how to do that, if somebody can explain me how, it will ...
user3464216
25
votes
3
answers
36k
views
Skip elements on a condition based in a list comprehension in python
I have a list List:
List = [-2,9,4,-6,7,0,1,-4]
For numbers less than zero (0) in the list , I would like to skip those numbers and form another list.
Example:-
List = [9,4,7,0,1]
This is a kind ...
- 752
24
votes
2
answers
45k
views
Splitting a list in a Pandas cell into multiple columns [duplicate]
I have a really simple Pandas dataframe where each cell contains a list. I'd like to split each element of the list into it's own column. I can do that by exporting the values and then creating a new ...
- 9,003
23
votes
3
answers
26k
views
Generate list of numbers in specific format
I need to generate a list of numbers in a specific format. The format is
mylist = [00,01,02,03,04,05,06,07,08,09,10,11,12,13,14,15]
#Numbers between 0-9 are preceded by a zero.
I know how to ...
- 49k
22
votes
5
answers
12k
views
Python: How RECURSIVELY remove None values from a NESTED data structure (lists and dictionaries)?
Here is some nested data, that includes lists, tuples, and dictionaries:
data1 = ( 501, (None, 999), None, (None), 504 )
data2 = { 1:601, 2:None, None:603, 'four':'sixty' }
data3 = OrderedDict( [(...
- 20k
22
votes
1
answer
12k
views
Should I use a Python deque or list as a stack? [duplicate]
I want a Python object that I can use as a stack. Is it better to use a deque or a list and does it make a difference whether I have a small number of elements or a large number of elements?
- 116k
22
votes
5
answers
23k
views
How to slice a list of tuples in python?
Assuming:
L = [(0,'a'), (1,'b'), (2,'c')]
How to get the index 0 of each tuple as the pretended result:
[0, 1, 2]
To get that I used python list comprehension and solved the problem:
[num[0] for ...
- 5,553
21
votes
3
answers
21k
views
Using Counter with list of lists
How would I use the Counter in the collections library to convert a list of lists into a count of the number of times each word occurs overall?
E.g. [['a','b','a','c'], ['a','b','c','d']] -> {a:2,...
- 257
21
votes
8
answers
7k
views
Constructing the largest number possible by rearranging a list
Say I have an array of positive whole integers; I'd like to manipulate the order so that the concatenation of the resultant array is the largest number possible. For example [97, 9, 13] results in ...
- 219
19
votes
6
answers
41k
views
Remove tuple from list of tuples if certain condition is met
I have a list of tuples that look like this;
ListTuples = [(100, 'AAA'), (80, 'BBB'), (20, 'CCC'), (40, 'DDD')]
I want to remove the tuples when the first element of the tuple is less than 50. The ...
- 27.2k
19
votes
4
answers
39k
views
How to determined if a 2 dimensional list contain a value?
I have a list like following
mylist = [('value1', 'value2', 'value3'), ('secval1', 'secval2', 'secval3')]
how do I see if the list contains 'value2'?
- 675
19
votes
3
answers
2k
views
Optimize the performance of dictionary membership for a list of Keys
I am trying to write a code which should return true if any element of list is present in a dictionary. Performance of this piece is really important. I know I can just loop over list and break if I ...
- 2,609
19
votes
13
answers
99k
views
Python 2.7 creating a multidimensional list
In Python I want an intuitive way to create a 3 dimensional list.
I want an (n by n) list. So for n = 4 it should be:
x = [[[],[],[],[]],[[],[],[],[]],[[],[],[],[]],[[],[],[],[]]]
I've tried using:...
- 223
18
votes
10
answers
33k
views
Iterate every 2 elements from list at a time
Having list as ,
l = [1,2,3,4,5,6,7,8,9,0]
How can i iterate every two elements at a time ?
I am trying this ,
for v, w in zip(l[:-1],l[1:]):
print [v, w]
and getting output is like ,
[1, ...
- 8,312
18
votes
2
answers
6k
views
Sort a list of lists by length and value in Python
How can I sort a Python list (with sublists)? For example, I have the following list:
list1 = [[0, 4, 1, 5], [3, 1, 5], [4, 0, 1, 5]]
After sorting I am expecting:
list1 = [[3, 1, 5], [0, 4, 1, 5], ...
- 453
18
votes
4
answers
43k
views
Unittest - Assert a set of items of a list are (or not) contained in another list
Hello I am new to programming and and trying to make a test that checks whether any items in a list of items are present in another list (using unittest in Python 2.7).
For example if I have a list ["...
- 185
18
votes
3
answers
38k
views
Python - set list range to a specific value
I need to set a subset of a list to a specific value based on a tuple with bounds (start,end).
Currently I'm doing this:
indexes = range(bounds[0], bounds[1] + 1)
for i in indexes:
my_list[i] = '...
- 18k
17
votes
7
answers
5k
views
Padding or truncating a Python list
I'd like to truncate or pad a list. E.g. for size 4:
[1,2,3] -> [1,2,3,0]
[1,2,3,4,5] -> [1,2,3,4]
I can see a couple of ways:
def trp(l, n):
""" Truncate or pad a list """
r = l[:n]
...
- 3,264
17
votes
6
answers
16k
views
flatten list of list through list comprehension
I am trying to flatten a list using list comprehension in python. My list is somewhat like
[[1, 2, 3], [4, 5, 6], 7, 8]
just for printing then individual item in this list of list I wrote this ...
- 4,959
17
votes
5
answers
19k
views
List on python appending always the same value [duplicate]
I have the following code inside a while loop.
if gender == 0 and len(men) < 51 :
height = float((random.uniform(1.3, 1.9) + (random.randint(10, 20)/100.)).__format__('.2f'))
weight = ...
- 1,224