Read list formatted data from file in python

Question

I know this must be a simple question for you all. I have textfile with test cases written in below list format,

[["arg1", "arg2", "arg3"], "Fail"]

[["arg1", "arg2", "arg4"], "Pass"]

. . .

And I want to read this file in a list such a that, I can print list1[1] => "Fail".

thanks for your help.

You need something like: `["arg1", "arg2", "arg3"]` => `"Fail"` ? — codrelphi, Jan 14 '20 at 10:26

score 3 · Accepted Answer · answered Jan 14 '20 at 11:04

3

You can use ast.literal_eval() to safe convert the string line to a python expression

Example:

import ast

with open('list.txt') as f:
    lines = f.readlines()

data = [ast.literal_eval(line) for line in lines]

for item in data:
    print(item[1])

answered Jan 14 '20 at 11:04

Sergey Tolokonnikov

54
3

Thanks, Sergey Tolokonnikov, I was trying this module but was doing some silly mistakes. – Pravin Junnarkar Jan 14 '20 at 16:30

score 2 · Answer 2 · answered Jan 14 '20 at 10:37

Assumptions

You have a .txt file.
Format of a line is [["arg1", "arg2", "arg3",...etc.], "Fail/Pass"]

Approach is to use regex to find all text between double quotes and append to the list. The last one is taken as "Fail/Pass" and rest of them are args.

import re

result = []

with open('text.txt','r') as f:
    for line in f:
        match = re.findall("\"(.*?)\"",line.strip())
        result.append([match[:-1],match[-1]])

print(result)
print(result[0][0])
print(result[0][1])

Sample Input .txt file

[["arg1", "arg2", "arg3","arg4"], "Fail"]
[["arg1", "arg2", "arg4"], "Pass"]

Output

[[['arg1', 'arg2', 'arg3', 'arg4'], 'Fail'], [['arg1', 'arg2', 'arg4'], 'Pass']]
['arg1', 'arg2', 'arg3', 'arg4']
Fail

Thanks Ajay. I liked your approach. – Pravin Junnarkar Jan 14 '20 at 16:12 — Pravin Junnarkar, Jan 14 '20 at 16:12

score 2 · Answer 3 · answered Jan 14 '20 at 10:55

2

Just use eval , its internal python function and you dont need libraries.

Example:

lists = []
line1 = '[["arg1", "arg2", "arg3"], "Fail"]'
line2 = '[["arg1", "arg2", "arg4"], "Pass"]'
# Evaluate Lines
exLine1 = eval(line1)
exLine2 = eval(line2)
# Append Lines to lists
lists.append(exLine1)
lists.append(exLine2)
# Testing Example of your use case
print(str(exLine1[1] == "Fail"))

Just Convert this example to for loop you are using and it will be fast and simple

answered Jan 14 '20 at 10:55

Jiri Otoupal イりオトウパー

591
3
15

1

You must never use `eval()` in python. Read [Why is using 'eval' a bad practice?](https://stackoverflow.com/questions/1832940/why-is-using-eval-a-bad-practice) – Ajay Dabas Jan 15 '20 at 03:38

Deepak Raj · Answer 4 · 2020-01-14T10:42:56.337

1

I would do like this.

sample myfile.txt:

[["arg1", "arg2", "arg3"], "Fail"]
[["arg1", "arg2", "arg4"], "Pass"]

Main python file.

file1 = open('myfile.txt', 'r') 
count = 0

while True: 
    count += 1

    # Get next line from file 
    list = file1.readline()
    if not list: 
        break
    #convert string to list
    res = list.strip('][').split(', ') 
    print(res[1])

After reading the file line by line, Convert the string of list into list by using split.

edited Jan 14 '20 at 10:42

answered Jan 14 '20 at 10:29

Deepak Raj

316
1
10

Hello Deepak, thanks for your try. But you are reading all values in one list whereas I need list format as is in text file. – Pravin Junnarkar Jan 14 '20 at 16:09
Please refer this link for converting string representation of list to list https://www.geeksforgeeks.org/python-convert-a-string-representation-of-list-into-list/ – Deepak Raj Jan 15 '20 at 14:47

score 1 · Answer 5 · answered Jan 14 '20 at 10:42

You can hack together some pretty simple string manipulation code, as everyone is providing here. I've done it simply like this:

text = """
[["arg1", "arg2", "arg3"], "Fail"]
[["arg1", "arg2", "arg4"], "Pass"]
"""

for line in text.strip().splitlines():
    line = line.replace('[', '')
    line = line.replace(']', '')
    print line.split(',')[-1].strip()

It's not pretty but you can do it plenty of better ways if you're looking to do this is production.

Nice try ev350. Thanks for helping. – Pravin Junnarkar Jan 14 '20 at 16:14 — Pravin Junnarkar, Jan 14 '20 at 16:14

score 1 · Answer 6 · edited Jan 22 '20 at 09:47

1

you can try something like below:

with open("test.txt", "r") as test_file:
content = test_file.readlines()

print(content)
print(type(content))

for data in content:
    print(ast.literal_eval(data)[1])

print("*" * 30)
for i in range(1, len(content)+1):
    print(i)

output:

index:  0

[["arg1", "arg2", "arg3"], "Fail"]

index: 1

[["arg1", "arg2", "arg4"], "Pass"]

1
2

edited Jan 22 '20 at 09:47

Ch3steR

20,090
4
28
58

answered Jan 14 '20 at 13:10

Nasreen Ustad

1,564
1
19
24

Thanks, Nasreen for trying, but this solution is not giving me proper elements. – Pravin Junnarkar Jan 14 '20 at 16:34

score 0 · Answer 7 · answered Jan 14 '20 at 10:25

0

What about this code example from link:

# load additional module
import pickle

with open('listfile.data', 'rb') as filehandle:
    # read the data as binary data stream
    placesList = pickle.load(filehandle)

answered Jan 14 '20 at 10:25

Mohammed Deifallah

1,290
1
10
25

I tried but it's not working... thanks for your help. – Pravin Junnarkar Jan 14 '20 at 16:05

Read list formatted data from file in python

7 Answers7