I have an integer and a list. I would like to make a new list of them beginning with the variable and ending with the list.
Writing a + list
I get errors. The compiler handles a
as integer, thus I cannot use append, or extend either.
How would you do this?
list_1.insert(0,ur_data)
make sure that ur_data is of string type
so if u have data= int(5)
convert it to ur_data = str(data)
None of these worked for me. I converted the first element to be part of a series (a single element series), and converted the second element also to be a series, and used append function.
l = ((pd.Series(<first element>)).append(pd.Series(<list of other elements>))).tolist()
>>> a = 5
>>> li = [1, 2, 3]
>>> [a] + li # Don't use 'list' as variable name.
[5, 1, 2, 3]
New lists can be made by simply adding lists together.
list1 = ['value1','value2','value3']
list2 = ['value0']
newlist=list2+list1
print(newlist)
Based on some (minimal) benchmarks using the timeit
module it seems that the following has similar if not better performance than the accepted answer
new_lst = [a, *lst]
As with [a] + list
this will create a new list and not mutate lst
.
If your intention is to mutate the list then use lst.insert(0, a)
.
You can use Unpack list:
a = 5
li = [1,2,3]
li = [a, *li]
=> [5, 1, 2, 3]
Another way of doing the same,
list[0:0] = [a]
>>> from collections import deque
>>> my_list = deque()
>>> my_list.append(1) # append right
>>> my_list.append(2) # append right
>>> my_list.append(3) # append right
>>> my_list.appendleft(100) # append left
>>> my_list
deque([100, 1, 2, 3])
>>> my_list[0]
100
[NOTE]:
collections.deque
is faster than Python pure list
in a loop Relevant-Post.
Note that if you are trying to do that operation often, especially in loops, a list is the wrong data structure.
Lists are not optimized for modifications at the front, and somelist.insert(0, something)
is an O(n) operation.
somelist.pop(0)
and del somelist[0]
are also O(n) operations.
The correct data structure to use is a deque
from the collections
module. deques expose an interface that is similar to those of lists, but are optimized for modifications from both endpoints. They have an appendleft
method for insertions at the front.
Demo:
In [1]: lst = [0]*1000
In [2]: timeit -n1000 lst.insert(0, 1)
1000 loops, best of 3: 794 ns per loop
In [3]: from collections import deque
In [4]: deq = deque([0]*1000)
In [5]: timeit -n1000 deq.appendleft(1)
1000 loops, best of 3: 73 ns per loop
Source: Stackoverflow.com