Eval list of strings python

There isn't any need to import anything or to evaluate. You can do this in one line for most basic use cases, including the one given in the original question.

One liner

l_x = [i.strip() for i in x[1:-1].replace('"',"").split(',')]

Explanation

x = '[ "A","B","C" , " D"]'
# String indexing to eliminate the brackets.
# Replace, as split will otherwise retain the quotes in the returned list
# Split to convert to a list
l_x = x[1:-1].replace('"',"").split(',')

Outputs:

for i in range(0, len(l_x)):
    print(l_x[i])
# vvvv output vvvvv
'''
 A
B
C
  D
'''
print(type(l_x)) # out: class 'list'
print(len(l_x)) # out: 4

You can parse and clean up this list as needed using list comprehension.

l_x = [i.strip() for i in l_x] # list comprehension to clean up
for i in range(0, len(l_x)):
    print(l_x[i])
# vvvvv output vvvvv
'''
A
B
C
D
'''

Nested lists

If you have nested lists, it does get a bit more annoying. Without using regex (which would simplify the replace), and assuming you want to return a flattened list (and the zen of python says flat is better than nested):

x = '[ "A","B","C" , " D", ["E","F","G"]]'
l_x = x[1:-1].split(',')
l_x = [i
    .replace(']', '')
    .replace('[', '')
    .replace('"', '')
    .strip() for i in l_x
]
# returns ['A', 'B', 'C', 'D', 'E', 'F', 'G']

If you need to retain the nested list it gets a bit uglier, but it can still be done just with regular expressions and list comprehension:

import re

x = '[ "A","B","C" , " D", "["E","F","G"]","Z", "Y", "["H","I","J"]", "K", "L"]'
# Clean it up so the regular expression is simpler
x = x.replace('"', '').replace(' ', '')
# Look ahead for the bracketed text that signifies nested list
l_x = re.split(r',(?=\[[A-Za-z0-9\',]+\])|(?<=\]),', x[1:-1])
print(l_x)
# Flatten and split the non nested list items
l_x0 = [item for items in l_x for item in items.split(',') if not '[' in items]
# Convert the nested lists to lists
l_x1 = [
    i[1:-1].split(',') for i in l_x if '[' in i
]
# Add the two lists
l_x = l_x0 + l_x1

This last solution will work on any list stored as a string, nested or not.

We may sometime get data which contains strings but the structure of the data inside the stream is a Python list. In this article we will convert string enclosed list to an actual Python list which can be further used in data manipulation.

With eval

We know the eval function will give us the actual result which is supplied to it as parameter. So so we supplied the given string to the eval function and get back the Python list.

Example

 Live Demo

stringA = "['Mon', 2,'Tue', 4, 'Wed',3]"
# Given string
print("Given string : \n",stringA)
# Type check
print(type(stringA))
# using eval
res = eval(stringA)
# Result
print("The converted list : \n",res)
# Type check
print(type(res))

Output

Running the above code gives us the following result −

Given string :
['Mon', 2,'Tue', 4, 'Wed',3]

The converted list :
['Mon', 2, 'Tue', 4, 'Wed', 3]

With ast.literal_eval

In this approach, we take the estimate and use the literal_eval function by giving it the string as a parameter. It gives back the Python list.

Example

 Live Demo

import ast
stringA = "['Mon', 2,'Tue', 4, 'Wed',3]"
# Given string
print("Given string : \n",stringA)
# Type check
print(type(stringA))
# using literal_eval
res = ast.literal_eval(stringA)
# Result
print("The converted list : \n",res)
# Type check
print(type(res))

Output

Running the above code gives us the following result −

Given string :
['Mon', 2,'Tue', 4, 'Wed',3]

The converted list :
['Mon', 2, 'Tue', 4, 'Wed', 3]

With json.loads

The loads function injection module can do a similar conversion where the string is evaluated and actual Python list is generated.

Example

 Live Demo

import json
stringA = '["Mon", 2,"Tue", 4, "Wed",3]'
# Given string
print("Given string : \n",stringA)
# Type check
print(type(stringA))
# using loads
res = json.loads(stringA)
# Result
print("The converted list : \n",res)
# Type check
print(type(res))

Output

Running the above code gives us the following result −

Given string :
["Mon", 2,"Tue", 4, "Wed",3]

The converted list :
['Mon', 2, 'Tue', 4, 'Wed', 3]

Updated on 04-Jun-2020 11:11:47

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