I created 2 lists in python `
ls = []
a = ['a','b','c','d','e','f']
i = 0
while i < 5:
x = a[-1]
a.pop(-1)
a.insert(0, x)
ls.insert(0, a)
i += 1
print(ls)
What I want to do is to add something from the list filled with letters into an empty list and making the result look like this
ls = [
['a','b','c','d','e','f'],
['f','a','b','c','d','e'],
['e','f','a','b','c','d'],
['d','e','f','a','b','c'],
['c','d','e','f','a','b'],
['b','c','d','e','f','a']
]
I would like to know where I made a mistake in python and the solution.
The list is a mutable object in python, so when you insert the list a in the ls, you are just adding a reference to the list a, instead of adding the whole value.
A workaround would be to insert a copy of a in the ls. One way to create a new copy of the list is using the list() on the list or you can use copy function from copy module. So doing ls.insert(0, a.copy()) would give the same result as below -
ls = []
a = ['a','b','c','d','e','f']
i = 0
while i < 5:
x = a[-1]
a.pop(-1)
a.insert(0, x)
ls.insert(0, list(a)) # updated this
i += 1
print(ls)
Output:
[['b', 'c', 'd', 'e', 'f', 'a'], ['c', 'd', 'e', 'f', 'a', 'b'], ['d', 'e', 'f', 'a', 'b', 'c'], ['e', 'f', 'a', 'b', 'c', 'd'], ['f', 'a', 'b', 'c', 'd', 'e']]
Another easy way to get your expected output would be to -
ls = []
a = ['a','b','c','d','e','f']
for i in range(6):
ls.append(a.copy())
a = [a[-1]] + a[:-1]
print(ls)
Output :
[['a', 'b', 'c', 'd', 'e', 'f'], ['f', 'a', 'b', 'c', 'd', 'e'], ['e', 'f', 'a', 'b', 'c', 'd'], ['d', 'e', 'f', 'a', 'b', 'c'], ['c', 'd', 'e', 'f', 'a', 'b'], ['b', 'c', 'd', 'e', 'f', 'a']]
Related
seats = 4 # user can choose an even input, I put 4 for this example
rows = 4 # user can choose an even or odd input, I put 4 for this example
seats_in_row_list = [i for i in string.ascii_uppercase[:seats]]
main_seat_list = [seats_in_row_list for i in range(rows)]
The output is:
[['A', 'B', 'C', 'D'], ['A', 'B', 'C', 'D'], ['A', 'B', 'C', 'D'], ['A', 'B', 'C', 'D']]
But when I try to change 'A' to 'X' in the first list all of the lists change:
[['X', 'B', 'C', 'D'], ['X', 'B', 'C', 'D'], ['X', 'B', 'C', 'D'], ['X', 'B', 'C', 'D']]
What I'm looking for is this output:
[['X', 'B', 'C', 'D'], ['A', 'B', 'C', 'D'], ['A', 'B', 'C', 'D'], ['A', 'B', 'C', 'D']]
Use copy method to have a copy of the individual list before assigning
main_seat_list = [seats_in_row_list.copy() for i in range(rows)]
If you aren't using seats_in_row_list for anything other than the construction of main_seat_list, you should just inline the definition. Calling list here would be simpler than using a list comprehension.
seats = 4
rows = 4
main_seat_list = [list(string.ascii_uppercase[:seats]) for i in range(rows)]
Say I have this input data
my_input_list = [[A],[A,B,C],[D],[D,E,F],[A,B,C,D,E,F],[A,C,E]]
items_that_appear_twice = [A,B,C]
items_that_appear_four = [D,E,F]
And I want to create an expansion such that some elements are only allowed to appear twice.
my_output_list = [
[A],[A],
[A,B,C],[A,B,C],
[D],[D],[D],[D],
[D,E,F],[D,E,F],[D,E,F],[D,E,F],
[A,B,C,D,E,F],[A,B,C,D,E,F],[D,E,F],[D,E,F],
[A,C,E],[A,C,E],[E],[E]]
I tired a few ideas and didn't find a really neat solution, like building lists of four and list.remove() from them which generated two empty lists.
For example list removal techniques on my_input_list[0]*4 gives [A],[A],[],[] (two empty lists) when I want [A],[A] .
I have a working version: See Pyfiddle.
my_input_list = [['A'],['A','B','C'],['D'],['D','E','F'],['A','B','C','D','E','F'],['A','C','E']]
items_that_appear_twice = ['A','B','C']
items_that_appear_four = ['D','E','F']
my_output_list = []
for my_input in my_input_list:
items_allowed_to_appear_twice = list(filter(
lambda value: (value in items_that_appear_twice
or value in items_that_appear_four),
my_input))
items_allowed_to_appear_four = list(filter(
lambda value: value in items_that_appear_four,
my_input))
my_output_list += 2*[items_allowed_to_appear_twice]
if len(items_allowed_to_appear_four):
my_output_list += 2*[items_allowed_to_appear_four]
print(my_output_list)
my_input_list = [['A'],
['A', 'B', 'C'],
['D'],
['D', 'E', 'F'],
['A', 'B', 'C', 'D', 'E', 'F'],
['A', 'C', 'E']]
items_that_appear_twice = ['A', 'B', 'C']
items_that_appear_four = ['D', 'E', 'F']
my_output_list = []
for sub in my_input_list:
my_output_list.append(sub)
my_output_list.append(sub)
sub = [x for x in sub if x in items_that_appear_four]
if sub:
my_output_list.append(sub)
my_output_list.append(sub)
assert my_output_list == [
['A'], ['A'],
['A', 'B', 'C'], ['A', 'B', 'C'],
['D'], ['D'], ['D'], ['D'],
['D', 'E', 'F'], ['D', 'E', 'F'], ['D', 'E', 'F'], ['D', 'E', 'F'],
['A', 'B', 'C', 'D', 'E', 'F'], ['A', 'B', 'C', 'D', 'E', 'F'], ['D', 'E', 'F'], ['D', 'E', 'F'],
['A', 'C', 'E'], ['A', 'C', 'E'], ['E'], ['E']]
Below is my solution, sort the sub list first, then append to the result according different situation.
my_input_list = [['A'],['A','B','C'],['D'],['D','E','F'],['A','B','C','D','E','F'],['A','C','E']]
items_that_appear_twice = ['A','B','C']
items_that_appear_four = ['D','E','F']
result = []
for sublist in my_input_list:
appearence = {1:[], 2:[], 4:[]}
for item in sublist:
appearence[2].append(item) if item in items_that_appear_twice else (appearence[4].append(item) if item in items_that_appear_four else appearence[1].append(item))
if len(appearence[2]) > 0:
result.append([appearence[2] + appearence[4]] * 2 + ([appearence[4]] * 2 if appearence[4] and len(appearence[4]) > 0 else []))
else:
result.append([appearence[4]] * 4)
for item in result:
print(item)
output:
[['A'], ['A']]
[['A', 'B', 'C'], ['A', 'B', 'C']]
[['D'], ['D'], ['D'], ['D']]
[['D', 'E', 'F'], ['D', 'E', 'F'], ['D', 'E', 'F'], ['D', 'E', 'F']]
[['A', 'B', 'C', 'D', 'E', 'F'], ['A', 'B', 'C', 'D', 'E', 'F'], ['D', 'E', 'F'], ['D', 'E', 'F']]
[['A', 'C', 'E'], ['A', 'C', 'E'], ['E'], ['E']]
[Finished in 0.178s]
Currently working on a 2D transposition cipher in Python. So I have a list that contains an encoded message, like below:
['BF', 'AF', 'AF', 'DA', 'CD', 'DD', 'BC', 'EF', 'DA', 'AA', 'EF', 'BF']
The next step is taking that list, splitting it up and putting it into a new matrix with regards to a keyword that the user enters. Which I have below:
Enter the keyword for final encryption: hide
H I D E
['B', 'F', 'A', 'F']
['A', 'F', 'D', 'A']
['C', 'D', 'D', 'D']
['B', 'C', 'E', 'F']
['D', 'A', 'A', 'A']
['E', 'F', 'B', 'F']
What I would like to do next and haven't done is take each of the columns above and print them in alphabetical order, therefore getting another cipher text, like below:
D E H I
['A', 'F', 'B', 'F']
['D', 'A', 'A', 'F']
['D', 'D', 'C', 'D']
['E', 'F', 'B', 'C']
['A', 'A', 'D', 'A']
['B', 'F', 'E', 'F']
Here's my code:
def encodeFinalCipher():
matrix2 = []
# Convert keyword to upper case
keywordKey = list(keyword.upper())
# Convert firstEncryption to a string
firstEncryptionString = ''.join(str(x) for x in firstEncryption)
# Print the first table that will show the firstEncryption and the keyword above it
keywordList = list(firstEncryptionString)
for x in range(0,len(keywordList),len(keyword)):
matrix2.append(list(keywordList[x:x+len(keyword)]))
# Print the matrix to the screen
print (' %s' % ' '.join(map(str, keywordKey)))
for letters in matrix2:
print (letters)
return finalEncryption
I have traversed the 2D matrix and got all the column entries like below:
b = [[matrix2[i][j] for i in range(len(matrix2))] for j in range(len(matrix2[0]))]
for index, item in enumerate (b):
print("\n",index, item)
OUTPUT:------
0 ['B', 'A', 'C', 'B', 'D', 'E']
1 ['F', 'F', 'D', 'C', 'A', 'F']
2 ['A', 'D', 'D', 'E', 'A', 'B']
3 ['F', 'A', 'D', 'F', 'A', 'F']
How would I append each letter of the keywordKey (e.g. 'H' 'I' 'D' 'E') to the list where the numbers 0,1,2,3 are?
Or probably a more efficient solution. How would I put the letters into the keywordKey columns when creating the matrix? Would a dictionary help here? Then I could sort the dictionary and print the final cipher.
Many thanks
You can do something like this:
>>> from operator import itemgetter
>>> from pprint import pprint
>>> lst = [['B', 'F', 'A', 'F'],
['A', 'F', 'D', 'A'],
['C', 'D', 'D', 'D'],
['B', 'C', 'E', 'F'],
['D', 'A', 'A', 'A'],
['E', 'F', 'B', 'F']]
>>> key = 'HIDE'
Sort xrange(len(key)) or range(len(key)) using the corresponding values from key and then you will have a list of indices:
>>> indices = sorted(xrange(len(key)), key=key.__getitem__)
>>> indices
[2, 3, 0, 1]
Now all we need to do is loop over the list and apply these indices to each item using operator.itemgetter and get the corresponding items:
>>> pprint([list(itemgetter(*indices)(x)) for x in lst])
[['A', 'F', 'B', 'F'],
['D', 'A', 'A', 'F'],
['D', 'D', 'C', 'D'],
['E', 'F', 'B', 'C'],
['A', 'A', 'D', 'A'],
['B', 'F', 'E', 'F']]
#or simply
>>> pprint([[x[i] for i in indices] for x in lst])
[['A', 'F', 'B', 'F'],
['D', 'A', 'A', 'F'],
['D', 'D', 'C', 'D'],
['E', 'F', 'B', 'C'],
['A', 'A', 'D', 'A'],
['B', 'F', 'E', 'F']]
This is my program to append list value into dictionary
lis=['a','b','c']
st=['d','e']
count=0
f={}
for s in st:
lis.append(s)
f[count]=lis
count+=1
print f
my expected output is
{0: ['a', 'b', 'c', 'd'], 1: ['a', 'b', 'c', 'd', 'e']}
but i got
{0: ['a', 'b', 'c', 'd', 'e'], 1: ['a', 'b', 'c', 'd', 'e']}
as output. Please help me to solve this. Thanks in advance.
You need to copy the list, because if you add it to the dictionary then modify it, it will change all the copies that exist in the dictionary.
import copy
l = ['a','b','c']
st = ['d','e']
count = 0
f = {}
for s in st:
l.append(s)
f[count] = copy.copy(l)
count += 1
print f
Output
{0: ['a', 'b', 'c', 'd']}
{0: ['a', 'b', 'c', 'd'], 1: ['a', 'b', 'c', 'd', 'e']}
lis=['a','b','c']
st=['d','e']
{ i :lis+st[:i+1] for i in range(0,2) }
#output ={0: ['a', 'b', 'c', 'd'], 1: ['a', 'b', 'c', 'd', 'e']}
Just copy the list before putting in f so that it's value doesn't change as you add elements to the original list:
f[count]= lis[:] # copy lis
and you get:
{0: ['a', 'b', 'c', 'd']}
{0: ['a', 'b', 'c', 'd'], 1: ['a', 'b', 'c', 'd', 'e']}
Note: Thanks to #PadraicCunningham for pointing out that [:] notation is faster than list() -- at least for small list (see What is the best way to copy a list? or How to clone or copy a list?).
I have a matrix:
matrix = [['F', 'B', 'F', 'A', 'C', 'F'],
['D', 'E', 'B', 'E', 'B', 'E'],
['F', 'A', 'D', 'B', 'F', 'B'],
['B', 'E', 'F', 'B', 'D', 'D']]
I want to remove and collect the first two elements of each sub-list, and add them to a new list.
so far i have got:
while messagecypher:
for vector in messagecypher:
final.extend(vector[:2])
the problem is; the slice doesn't seem to remove the elements, and I end up with a huge list of repeated chars. I could use .pop(0) twice, but that isn't very clean.
NOTE: the reason i remove the elements is becuase i need to keep going over each vector until the matrix is empty
You can keep your slice and do:
final = []
for i in range(len(matrix)):
matrix[i], final = matrix[i][:2], final + matrix[i][2:]
Note that this simultaneously assigns the sliced list back to matrix and adds the sliced-off part to final.
Well you can use a list comprehension to get the thing done, but its perhaps counter-intuitive:
>>> matrix = [['F', 'B', 'F', 'A', 'C', 'F'],
['D', 'E', 'B', 'E', 'B', 'E'],
['F', 'A', 'D', 'B', 'F', 'B'],
['B', 'E', 'F', 'B', 'D', 'D']]
>>> while [] not in matrix: print([i for var in matrix for i in [var.pop(0), var.pop(0)]])
['F', 'B', 'D', 'E', 'F', 'A', 'B', 'E']
['F', 'A', 'B', 'E', 'D', 'B', 'F', 'B']
['C', 'F', 'B', 'E', 'F', 'B', 'D', 'D']
EDIT:
Using range makes the syntax look cleaner:
>>> matrix = [['C', 'B', 'B', 'D', 'F', 'B'], ['D', 'B', 'B', 'A', 'B', 'A'], ['B', 'D', 'E', 'F', 'C', 'B'], ['B', 'A', 'C', 'B', 'E', 'F']]
>>> while [] not in matrix: print([var.pop(0) for var in matrix for i in range(2)])
['C', 'B', 'D', 'B', 'B', 'D', 'B', 'A']
['B', 'D', 'B', 'A', 'E', 'F', 'C', 'B']
['F', 'B', 'B', 'A', 'C', 'B', 'E', 'F']
Deleting elements is not an efficient way to go about your task. It requires Python to perform a lot of unnecessary work shifting things around to fill the holes left by the deleted elements. Instead, just shift your slice over by two places each time through the loop:
final = []
for i in xrange(0, len(messagecypher[0]), 2):
for vector in messagecypher:
final.extend(vector[i:i+2])