Python: error parsing strings from text file with Ast module

Question

I have a text file (.txt) with the following two strings as so (this is a snippet of a larger file where all strings have the same format):

["('a', '1')", "('b', '2')"]
["('c', '3')", "('d', '4')"]

I am using the below code to parse the strings in the text file so that I can access each element for data analysis. The code works for the string if I declare it as a variable, such as:

string = ["('c', '3')", "('d', '4')"]

But the code does not work for the text file:

import ast

text_file = open('text_file.txt', 'r')

for string in text_file:
    parsed = list([ast.literal_eval(x) for x in text_file])
    print parsed

I would expect to get:

[('a', '1'), ('b', '2')]
[('c', '3'), ('d', '4')]

But I get the following error:

Traceback (most recent call last):
  File "test.py", line 8, in <module>
    parsed = list([ast.literal_eval(x) for x in string])
  File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ast.py", line 49, in literal_eval
    node_or_string = parse(node_or_string, mode='eval')
  File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ast.py", line 37, in parse
    return compile(source, filename, mode, PyCF_ONLY_AST)
  File "<unknown>", line 1
    [
    ^
SyntaxError: unexpected EOF while parsing

I couldn't reproduce the problem. It works fine. – thefourtheye Mar 26 '15 at 02:37 — thefourtheye, Mar 26 '15 at 02:37

Avinash Raj · Accepted Answer · 2015-03-26T02:35:46.353

2

You need to apply ast.literal_eval function on the string itself. You don't need to iterate over the contents of the string.

with open('file') as f:
    for string in f:
        parsed = ast.literal_eval(string.strip())
        print parsed

Output:

["('a', '1')", "('b', '2')"]
["('c', '3')", "('d', '4')"]

OR

import re
with open('file') as f:
    for string in f:
        print re.findall(r"\('([^']*)',\s*'([^']*)'\)", string)

Output:

[('a', '1'), ('b', '2')]
[('c', '3'), ('d', '4')]

edited Mar 26 '15 at 02:35

answered Mar 26 '15 at 02:30

Avinash Raj

172,303
28
230
274

Thanks Raj, but how do I gain access to each element for data analysis? I need to be able to, for example, output only the value associated with a. – Steve Mar 26 '15 at 02:37
ast.literal_eval does a single time conversion. That's why i also added another option. – Avinash Raj Mar 26 '15 at 02:41
Got it, the second option works. If there is anyway to get the first option to work, I'd be curious to see it; otherwise no big deal. Thanks! – Steve Mar 26 '15 at 02:46

score 0 · Answer 2 · answered Mar 26 '15 at 02:32

0

import ast 

text_file = open('text_file.txt', 'r')

for string in text_file:
    print ast.literal_eval(string)

answered Mar 26 '15 at 02:32

Vinod Sharma

883
6
13

Python: error parsing strings from text file with Ast module

2 Answers2

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