How to create list of nested dictionaries from file

Question

I have an input text file containing a list of key/value pairs that I would like to read into python as a list of dictionaries but can not seem to get it to work as expected. Note that the file is not in valid json format so I can not use the json built-in and this question is not a duplicate of this. I suspect that I am missing something obvious here so any guidance is much appreciated.

# /tmp/tmp.txt
[{'k1': {'k2': {'k3': ['a', 'b', 'c']}}}, {'k4': {'k5': {'k6': ['v', 'x', 'y', 'z']}}}]

Since this file contains a list with 2 elements, I would expect the len to be 2 and the type to be list but that is not what I'm seeing.

with open('/tmp/tmp.txt', encoding='utf-8') as data_file:
    data = data_file.read()

print(len(data)) # <-- the goal is for this to show 2
print(type(data)) # <-- the goal is for this to return `list`

Output:

88
<class 'str'>

data_file.read() does just return a string. I doesn't automatically convert your file to a list. :) — Vincent Pakson, Oct 12 '18 at 03:52

score 2 · Accepted Answer · answered Oct 12 '18 at 03:37

2

Your data is a string. You can convert it to a list with literal_eval:

import ast
data_list = ast.literal_eval(data)
len(data_list)
#2

answered Oct 12 '18 at 03:37

DYZ

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Thanks for this. I was not previously aware of the `ast` library and will check it out further. – user9074332 Oct 17 '18 at 02:55

Shai Léger · Answer 2 · 2018-10-12T03:48:07.837

EDIT: I didn't saw earlier that DYZ answered before me but I would like to explain my answer a bit more.

There is a module called 'ast' that have the function 'literal_eval', as the name suggest, it evaluates the information of the txt as python code and also validates the input.

import os, ast

with open('/tmp/tmp.txt', encoding='utf-8') as data_file:
    data = ast.literal_eval(data_file.read())

print(len(data))
print(type(data))

Output:

2
<class 'list'>

How to create list of nested dictionaries from file

Output:

2 Answers2