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How do I sort a text file after the last instance of a character?

Goal: Sort the text file alphabetically based on the characters that appear AFTER the final slash. Note that there are random numbers right before the final slash.
Contents of the text file:
https://www.website.com/1939332/delta.html
https://www.website.com/2237243/alpha.html
https://www.website.com/1242174/zeta.html
https://www.website.com/1839352/charlie.html
Desired output:
https://www.website.com/2237243/alpha.html
https://www.website.com/1839352/charlie.html
https://www.website.com/1939332/delta.html
https://www.website.com/1242174/zeta.html
Code Attempt:
i = 0
for line in open("test.txt").readlines(): #reading text file
List = line.rsplit('/', 1) #splits by final slash and gives me 4 lists
dct = {list[i]:list[i+1]} #tried to use a dictionary
sorted_dict=sorted(dct.items()) #sort the dictionary
textfile = open("test.txt", "w")
for element in sorted_dict:
textfile.write(element + "\n")
textfile.close()
Code does not work.

I would pass a different key function to the sorted function. For example:
with open('test.txt', 'r') as f:
lines = f.readlines()
lines = sorted(lines, key=lambda line: line.split('/')[-1])
with open('test.txt', 'w') as f:
f.writelines(lines)
See here for a more detailed explanation of key functions.

Before you run this, I am assuming you have a newline at the end of your test.txt. This will fix "combining the second and third lines".
If you really want to use a dictionary:
dct = {}
i=0
with open("test.txt") as textfile:
for line in textfile.readlines():
mylist = line.rsplit('/',1)
dct[mylist[i]] = mylist[i+1]
sorted_dict=sorted(dct.items(), key=lambda item: item[1])
with open("test.txt", "w") as textfile:
for element in sorted_dict:
textfile.write(element[i] + '/' +element[i+1])
What you did wrong
In the first line, you name your variable List, and in the second you access it using list.
List = line.rsplit('/', 1)
dct = {list[i]:list[i+1]}
Variable names are case sensitive so you need use the same capitalisation each time. Furthermore, Python already has a built-in list class. It can be overridden, but I would not recommend naming your variables list, dict, etc.
( list[i] will actually just generate a types.GenericAlias object, which is a type hint, something completely different from a list, and not what you want at all.)
You also wrote
dct = {list[i]:list[i+1]}
which repeatedly creates a new dictionary in each loop iteration, overwriting whatever was stored in dct previously. You should instead create an empty dictionary before the loop, and assign values to its keys every time you want to update it, as I have done.
You're calling sort in each iteration in the loop; you should only call once it after the loop is done. After all, you only want to sort your dictionary once.
You also open the file twice, and although you close it at the end, I would suggest using a context manager and the with statement as I have done, so that file closing is automatically handled.
My code
sorted(dct.items(), key=lambda item: item[1])
means that the sorted() function uses the second element in the item tuple (the dictionary item) as the 'metric' by which to sort.
`textfile.write(element[i] + '/' +element[i+1])`
is necessary, since, when you did rsplit('/',1), you removed the /s in your data; you need to add them back and reconstruct the string from the element tuple before you write it.
You don't need + \n in textfile.write since readlines() preserves the \n. That's why you should end text files with a newline: so that you don't have to treat the last line differently.

def sortFiles(item):
return item.split("/")[-1]
FILENAME = "test.txt"
contents = [line for line in open(FILENAME, "r").readlines() if line.strip()]
contents.sort(key=sortFiles)
with open(FILENAME, "w") as outfile:
outfile.writelines(contents)

Nested lists in python containing a single string and not single letters

I need to load text from a file which contains several lines, each line contains letters separated by coma, into a 2-dimensional list. When I run this, I get a 2 dimensional list, but the nested lists contain single strings instead of separated values, and I can not iterate over them. how do I solve this?
def read_matrix_file(filename):
matrix = []
with open(filename, 'r') as matrix_letters:
for line in matrix_letters:
line = line.split()
matrix.append(line)
return matrix
result:
[['a,p,p,l,e'], ['a,g,o,d,o'], ['n,n,e,r,t'], ['g,a,T,A,C'], ['m,i,c,s,r'], ['P,o,P,o,P']]
I need each letter in the nested lists to be a single string so I can use them.
thanks in advance

split() function splits on white space by default. You can fix this by passing the string you want to split on. In this case, that would be a comma. The code below should work.
def read_matrix_file(filename):
matrix = []
with open(filename, 'r') as matrix_letters:
for line in matrix_letters:
line = line.split(',')
matrix.append(line)
return matrix

The input format you described conforms to CSV format. Python has a library just for reading CSV files. If you just want to get the job done, you can use this library to do the work for you. Here's an example:
Input(test.csv):
a,string,here
more,strings,here
Code:
>>> import csv
>>> lines = []
>>> with open('test.csv') as file:
... reader = csv.reader(file)
... for row in reader:
... lines.append(row)
...
>>>
Output:
>>> lines
[['a', 'string', 'here'], ['more', 'strings', 'here']]

Using the strip() function will get rid of the new line character as well:
def read_matrix_file(filename):
matrix = []
with open(filename, 'r') as matrix_letters:
for line in matrix_letters:
line = line.split(',')
line[-1] = line[-1].strip()
matrix.append(line)
return matrix

Python - Read in Comma Separated File, Create Two lists

New to Python here and I'm trying to learn/figure out the basics. I'm trying to read in a file in Python that has comma separated values, one to a line. Once read in, these values should be separated into two lists, one list containing the value before the "," on each line, and the other containing the value after it.
I've played around with it for quite a while, but I just can't seem to get it.
Here's what I have so far...
with open ("mid.dat") as myfile:
data = myfile.read().replace('\n',' ')
print(data)
list1 = [x.strip() for x in data.split(',')]
print(list1)
list2 = ?
List 1 creates a list, but it's not correct. List 2, I'm not even sure how to tackle.
PS - I have searched other similar threads on here, but none of them seem to address this properly. The file in question is not a CSV file, and needs to stay as a .dat file.
Here's a sample of the data in the .dat file:
113.64,889987.226
119.64,440987774.55
330.43,446.21
Thanks.

Use string slicing:
list1= []
list2 = []
with open ("mid.dat") as myfile:
for line in myfile:
line = line.split(",").rstrip()
list1.append( line[0])
list2.append( line[1])
Python's rstrip() method strips all kinds of trailing whitespace by default, so removes return carriage "\n" too

If you want to use only builtin packages, you can use csv.
import csv
with open("mid.dat") as myfile:
csv_records = csv.reader(myfile)
list1 = []
list2 = []
for row in csv_records:
list1.append(row[0])
list2.append(row[1])

Could try this, which creates lists of floats not strings however:
from ast import literal_eval
with open("mid.dat") as f:
list1, list2 = map(list, (zip(*map(literal_eval, f.readlines()))))
Can be simplified if you don't mind list1 and list2 as tuples.
The list(*zip(*my_2d_list)) pattern is a pretty common way of transposing 2D lists using only built-in functions. It's useful in this scenario because it's easy to obtain a list (call this result) of tuples on each line in the file (where result[0] would be the first tuple, and result[n] would be the nth), and then transpose result (call this resultT) such that resultT[0] would be all the 'left values' and resultT[1] would be the 'right values'.

let's keep it very simple.
list1 = []
list2 = []
with open ("mid.dat") as myfile:
for line in myfile:
x1,x2 = map(float,line.split(','))
list1.append(x1)
list2.append(x2)
print(list1)
print(list2)

You could do this with pandas.
import pandas as pd
df = pd.read_csv('data.csv', columns=['List 1','List 2'])
If your data is a text file the respective function also exists in the pandas package. Pandas is a very powerful tool for data such as yours.
After doing so you can split your data into two independent dataframes.
list1 = df['List 1']
list2 = df['List 2']
I would stick to a dataframe because data manipulation and analysis is much easier within the pandas framework.

Here is my suggestion to be short and readable, without any additional packages to install:
with open ("mid.dat") as myfile:
listOfLines = [line.rstrip().split(',') for line in myfile]
list1 = [line[0] for line in listOfLines]
list2 = [line[1] for line in listOfLines]ility
Note: I used rstrip() to remove the end of line character.

Following is a solution obtained by correcting your own attempt:
with open("test.csv", "r") as myfile:
datastr = myfile.read().replace("\n",",")
datalist = datastr.split(",")
list1 = []; list2=[]
for i in range(len(datalist)-1): # ignore empty last item of list
if i%2 ==0:
list1.append(datalist[i])
else:
list2.append(datalist[i])
print(list1)
print(list2)
Output:
['113.64', '119.64', '330.43']
['889987.226', '440987774.55', '446.21']

Writing python two-level loop comprehension

I have an input file that contains lines of:
key \t value1 \t value2 .....
I'd like read this file into a dictionary where key is the first token of the line and the value is the list of the values.
I think something like this would do it, but python gives me an error that name l is not defined. How do I write a comprehension that has two levels of "for" statements like this?
f = open("input.txt")
datamap = {tokens[0]:tokens[1:] for tokens in l.split("\t") for l in enumerate(f)}

Use the csv module and insert each row into a dictionary:
import csv
with open('input.txt') as tsvfile:
reader = csv.reader(tsvfile, delimiter='\t')
datamap = {row[0]: row[1:] for row in reader}
This sidesteps the issue altogether.
You can put a str.split() result into a tuple to create a 'loop variable':
datamap = {row[0]: row[1:] for l in f for row in (l.strip().split("\t"),)}
Here row is bound to the one str.split() result from the tuple, effectively creating a row = l.strip().split('\t') 'assignment'.

Martijn's got you covered for improving the process, but just to directly address the issues you were seeing with your code:
First, enumerate is not doing what you think it's doing (although I'm not entirely sure what you think it's doing). You can just get rid of it.
Second, Python is trying to resolve this:
tokens[0]:tokens[1:] for tokens in l.split("\t")
before it sees what you're defining l as. You can put parentheses around the second comprehension to make it evaluate as you intended:
datamap = {tokens[0]:tokens[1:] for tokens in (l.split("\t") for l in f)}

Create list of tuples (in a more elegant way)

I am writing a python script to read a file which consists of three columns separated by commas, create a tuple of each line, and make a list of these tuples. With the following script I achieve what I want; I was just wondering whether there is an easier / more elegant approach than writing each of the following steps in a seperate line.
import sys
fin=open(sys.argv[1],'r')
list = []
for line1 in fin:
line2 = line1[:-1]
line3 = line2.split(',')
line4 = tuple(line3)
list.append(line4)
print(list)
Thank you for your answers.

Using a list comprehension:
lst = [tuple(line.rstrip().split(',')) for line in fin]
(Don't name your variables list; it shadows the built-in and can lead to unexpected bugs).

Python comes with batteries included! If you need to read csv files, just use the csv module:
import sys, csv
with open(sys.argv[1]) as f:
lst = list(csv.reader(f))
Note that this creates a list of lists, if you want tuples for some reason, then
with open(sys.argv[1]) as f:
lst = [tuple(row) for row in csv.reader(f)]