Python - open file - readline - list - convert to string

Question

The Issue/Question Details

I have a file (blah.txt) where its contents (a list) look like this:

Key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']

Inside of a simple python file (called CAT.py) I execute the following commands:

infile = open('blah.txt', 'r')
Key1 = infile.readline()
infile.close()
Key1 = Key1.rstrip('\n')
print(Key1)

Key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']

print(''.join(Key1))

Key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' '] <---- THIS IS WHAT I DO NOT WANT

However….

If in a separate simple python file (called DOG.py) I execute the following commands on a list:

Key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']

print(Key1)

['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', ' ']

print(''.join(Key1))

ABCDEFGHIJKLMNOPQRSTUVWXYZ <---- THIS IS WHAT I WANT

The Issue/Question

I ultimately want the output that looks like “ABCDEFGHIJKLMNOPQRSTUVWXYZ”, but for the life of me I cannot figure out how to read in a list for a file and then convert that list to a single string of characters. Can someone tell me where I am going wrong and also show me some code that would fix my problem?

Answer 1

You have to transform the string to a list before you can apply join .

First we use partition to get the part after the = . Then ast.literal_eval will create a list out of the string.

import ast
line = "Key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']"
data = line.partition('=')[2].strip()
elements = ast.literal_eval(data)
print(''.join(elements))

Additional: You could use with in the context of opening the file. If you do it, Python will close the file for you.

with open('blah.txt', 'r') as infile:
    line = infile.readline()

As jamylak pointed out: If you control the file please don't store the data like this. As you can see it's not easy to handle. You could store and read the data as JSON.

Answer 2

infile = open('blah.txt', 'r')
Key1 = infile.read()
import re
y=re.findall(r"([a-zA-Z])",Key1.split("=")[1])
print "".join(y)

You can simply try this.

Answer 3

>>> infile = open('blah.txt', 'r')
>>> key1 = infile.readline()
>>> infile.close()
>>> key1 = "Key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']"
>>> key1 = key1[key1.index('['):key1.index(']')+1]
>>> key1
"['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']"
>>> ''.join(eval(key1))
'ABCDEFGHIJKLMNOPQRSTUVWXYZ '

Answer 4

use ast.literal_eval .

import ast
with open('blah.txt') as f:
    for line in f:   # line = 'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' '.
        print ''.join(ast.literal_eval(line))

use str.split and split by = and then select the list of characters by indexing [-1] will gives you last index which carry the list of characters and then use ast.literal_eval to get the character and then use str.join to join all the characters.

import ast
with open('blah.txt') as f:
    for line in f:  # if line = key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']
        print ''.join(ast.literal_eval(line.split(' = ')[-1]))

Answer 5

YOur problem is that in your first example key1 is a string and not a list. The following should give you the desired output:

str_input = "Key1 = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' ']"

remove_unnecessary_data = str_input[str_input.find('[')+1: str_input.find(']')]

answer = ''.join([char for char in remove_unnecessary_data  if char not in("'", ",")])

Answer 6

import re

string = ""

read = open('blah.txt', 'r')

key = read.readline()

a = re.compile("[AZ]")

for char in key:

    if a.match(char):

            string = string + char

print string